Testicular Heat Stress and Sperm Quality 8

Damayanthi Durairajanayagam , Rakesh K. Sharma , Stefan S. du Plessis , and Ashok Agarwal

(such as elephants and rhinoceroses) and aquatic Introduction mammals (such as whales and dolphins) have intra-abdominal testes throughout their lifespan. In the male, exposure to heat has a deleterious The abdomen is metabolically active and it effect on fertility and is considered a signifi cant therefore generates a lot of heat. However, risk factor for male infertility [ 1]. Testicular tem- spermatogenesis functions optimally in these peratures should ideally be hypothermic compared mammals despite the proximity of their testes to to the core body temperature of 36.9 ¡C. This is the abdomen. essential for maintaining normal spermatogenesis Humans, on the other hand, have intra-scrotal and ideal sperm characteristics. A crucial feature testes that develop within the abdomen and, that contributes towards this is the anatomical posi- towards the end of the gestation period, begins its tion of the human testes, which is located outside descent through the inguinal canals into the scro- the body. Homeothermic animals have the ability tum. In humans, normal testicular function is to maintain a stable core body temperature despite temperature dependent and the extra-abdominal fl uctuating environmental temperatures. This is testes are maintained at temperatures below that achieved by regulating heat production and loss by of core body temperature [2 ]. Under normal means of adjusting the body’s metabolism. healthy environmental conditions, testicular ther- In most homeothermic birds and mammals, moregulation maintains scrotal hypothermy to including humans, testicular function depends on ensure optimal testicular function [1 ]. temperature. Temperatures that either fall below or above the physiological range required for optimal testicular function could potentially dis- Testicular Thermoregulation rupt spermatogenesis. Certain land mammals The normal physiological temperature of the human testis ranges between 32 and 35 ¡C [ 3 ]. Thermoregulation in the testis occurs via two D. Durairajanayagam , PhD ¥ R. K. Sharma , PhD ¥ A. Agarwal , PhD (*) mechanisms: the physiological properties of the Center for Reproductive Medicine, Cleveland Clinic , scrotum and the counter-current mechanism. Cleveland , OH , USA The scrotum is a loose sac-like structure that e-mail: [email protected] houses each testicle. The main function of the S. S. du Plessis , BSc (Hons), MSc, MBA, PhD (Stell) scrotum in most mammals is to prevent heat from Division of Medical Physiology, Department of reaching at the testis by means of adjusting to Biomedical Sciences, Faculty of Medicine and Health Sciences, Stellenbosch University , heat stress [ 4 ]. The scrotum has features that Tygerberg , Western Cape , South Africa allow free dissipation of heat through passive

S.S. du Plessis et al. (eds.), Male Infertility: A Complete Guide to Lifestyle and Environmental Factors, 105 DOI 10.1007/978-1-4939-1040-3_8, © Springer Science+Business Media New York 2014 106 D. Durairajanayagam et al. convection and radiation. These include a large loss. Conversely, when ambient temperatures total skin surface area that changes according to increase, the dartos and cremasteric muscles the surrounding temperature, a large number of relax causing the testes to lower away from the sweat glands, minimal subcutaneous fat, and body and the scrotal skin to become looser around sparse hair. When external temperatures rise and the testes, aiding heat loss. cause the scrotal temperature to increase beyond a threshold value, cutaneous receptors on the scrotal skin are activated, initiating secretions of Mechanism of Heat Stress: the scrotal sweat glands and active heat loss Testicular and Germ Cell Changes occurs through the evaporation of sweat [4 , 5 ]. Vasodilation of the scrotal vessels, the very thin Germ cells have high mitotic activity, which scrotal skin and the near-absence of surface hair makes them more susceptible to heat stress [8 ]. further contribute to heat dissipation. The type of germ cells that is most sensitive to The spermatic cord is made up of the testicu- heat is the pachytene and diplotene spermatocytes lar artery, veins, cremaster muscle, and vas defer- and early round spermatids in both the rat [ 9, 10 ] ens. The testicular artery is greatly coiled while and in humans [11 ]. In fact, the spermatogenic the veins have thin walls and poor musculariza- process, particularly the differentiation and matu- tion. The bulk of the spermatic cord is composed ration of spermatocytes and spermatids, is tem- of numerous testicular veins that anastomose and perature dependent and occurs ideally at a drain into the convoluted pampiniform plexus temperature of at least 1Ð2 ¡C below core body [ 6]. The testicular arterial and venous blood ves- temperature [1 , 10 ]. As such, raising the scrotal sels are intimately associated with each other, temperature causes testicular germinal epithelial facilitating the transfer of heat between the atrophy and spermatogenic arrest [12 ], leading to infl owing arterial blood to the outfl owing venous lower sperm counts. The supportive role of Sertoli blood in the spermatic cord. Thus, the arterial [ 13 ] and Leydig [ 14 ] cells towards germ cell blood arriving at the testis is effectively cooled development are also impacted by heat stress. while the venous blood disperses this heat Levels of a biochemical marker of spermatogene- through the scrotal skin [7 ]. In a normal individ- sis, inhibin B [ 15], decrease along with sperm ual, this counter-current heat exchange regulates concentration when scrotal temperatures are high the temperature of the arterial blood supply to the [ 16]. Irreversible testicular weight loss follows testis and epididymis at 2Ð4 ¡C below rectal tem- shortly after heat exposure [17 ]. Histopathological perature [7 ]. changes in the testis following heat exposure Thermoregulation of the testis is further aided include degeneration of the mitochondria, dilata- by two muscles: the cremasteric and dartos mus- tion of the smooth endoplasmic reticulum, and cles. The cremaster muscle is skeletal-type mus- wider intercellular spaces in both Sertoli and sper- cle that is associated with the spermatic cord and matid cells [18 ]. testis. A refl ex contraction of the cremasteric The fundamental mechanism by which loss of muscle can be produced by gently stroking the germ cells occurs in response to heat stress is due skin on the medial side of the thigh (cremasteric to apoptosis [9 , 19 ]. The intensity of heat stress refl ex). The dartos muscle is a layer of smooth and duration of heat exposure infl uence germ cell muscle fi bers that surround the testis subcutane- apoptosis. For example, 2 days after a single ously. When the ambient temperature falls, both exposure to heat (43 ¡C for 15 min), late pachy- the cremaster and the dartos muscles contract tene and early spermatids degenerate [ 20 ]. involuntarily, raising the testes and bringing them However, shorter heat exposure of the rat testes closer to the warmer body. The scrotal skin wrin- (43 ¡C for 10 min) does not result in apoptotic kles with the contraction of these muscles, reduc- germ cells whereas a longer heat exposure (43 ¡C ing the exposed surface area to avoid further heat for 30 min) intensifi es germ cell apoptosis [21 ]. 8 Testicular Heat Stress and Sperm Quality 107

Fig. 8.1 Schematic highlighting various mechanisms by which testicular heat stress causes germ cell apoptosis, DNA damage in mature and immature sperm and male infertility

Similarly, higher heat exposure (45 ¡C for mentally cryptorchid rats, heat stress (due to 15 min) causes generalized, nonspecifi c damage increased scrotal temperatures) increases genera- to many different germ cell types in adult rats. tion of reactive oxygen species leading to oxida- Besides apoptosis, heat stress also causes tive stress [ 23 , 24 ]. Moreover, in adult rats, the defects in DNA synapsis and DNA strand breaks effects of scrotal hyperthermia (43 ¡C for 30 min in pachytene spermatocytes and induces DNA once daily for 6 consecutive days) include damage in mature spermatozoa [20 ]. Sperm DNA decreased levels of glutathione, superoxide dis- damage that occurs in the heat-stressed testis is mutase, and glutathione peroxidase and increased likely due to excessive generation of reactive lipid peroxidation in the testes [18 ]. Further, gene oxygen species (which causes the sperm cell to expression for DNA repair and cellular antioxi- be in a state of oxidative stress) as well impaired dants are suppressed during testicular heat stress DNA repair in the germ cells [20 , 22 ]. In experi- [25 ] (Fig. 8.1 ). 108 D. Durairajanayagam et al.

In summary, heat-induced changes due to also suppressed in the hyperthermic testis [ 32 ]. increased scrotal temperatures in the testes lead Exposure to high temperature causes deteriora- to apoptosis of germ cells and sperm DNA dam- tion in sperm morphology and impairs motility as age, which subsequently suppresses spermato- well as sperm production, all of which have a del- genesis [18 , 20 ]. eterious effect on male fertility [33 , 34 ].

Impact of Failed Thermoregulation Pathological Failure on Semen Parameters of Thermoregulation

Semen analysis is carried out as a routine labora- Increased testicular temperatures due to either tory assessment of the infertile male. Fundamental endogenous or exogenous stimuli decrease sperm sperm parameters evaluated during a standard concentration, motility, and the number of mor- semen analysis include sperm concentration, phologically normal sperm [ 11 , 35 ]. Pathophys- motility, and morphology [26 ]. The total count iological abnormalities such as varicocele and and concentration of sperm refl ect semen quality cryptorchidism cause testicular hyperthermia, and the male reproductive potential whereas which could lead to male infertility [36 ]. Thus, sperm concentration and motility are best able to any disruption (either acute or chronic) to the predict fertility [27 ]. Repeated testicular expo- thermoregulation of the testis would have severe sure to elevated levels of heat could lead to adverse effects on the spermatogenic process. chronic thermo-dysregulation, which in time could lead to signifi cant changes in sperm char- acteristics [1 , 28 ]. Febrile Episodes Mean scrotal temperature is higher in infertile men than in fertile ones [29 ], and the higher the When the hypothalamic thermoregulation of the scrotal temperature, the more sperm quality is core body temperature is compromised with altered [29 ]. Men (mean age 31.8 years) who the onset of fever, thermoregulation at the level of were infertile for at least 2 years (without female the testes is also impacted. In a case study of a factor infertility) were found to have lower sperm fertile patient with infl uenza who was febrile count, percentage of motile sperm and testicular (39.9 ¡C) for 1 day, semen samples analyzed volume in both testes and higher mean scrotal 18Ð66 days post fever showed underlying effects temperatures compared to fertile men [ 29 ]. on sperm chromatin structure and a temporary However, testicular hyperthermia causes modifi - release of abnormal sperm [ 37 ]. In another study, cation of sperm characteristics in both the fertile the incidence of fever was reported to have a sig- and infertile male [29 ]. Physiological increases in nifi cant effect on spermatogenesis, and the more scrotal temperature are associated with substan- days of fever (between 1 and 11 days); the more tially reduced sperm concentration that results in increasingly adverse were its effects on sperm poor semen quality [30 ]. An increase of 1 ¡C concentration, percentage of normal and immo- above baseline values suppresses spermatogene- tile sperm [11 ]. Certain stages of spermatogenesis sis by 14 %, decreasing sperm production [31 ]. were found to be more predisposed to the effects Elevated testicular and epididymal tempera- of higher temperatures caused by a fever than oth- tures decrease the synthesis of sperm membrane ers: sperm concentration was affected when fever coating protein, resulting in higher amounts of occurred during meiosis (33Ð56 days before morphologically abnormal sperm [31 ]. Within ejaculation) and spermiogenesis (post-meiotic 6Ð8 months of exposure to elevated temperatures, phase, 9Ð32 days before ejaculation) while sperm the mean value of sperm with abnormal morphol- morphology and motility were affected when ogy was found to double [ 31]. Sperm motility is fever occurred during spermiogenesis [11 ]. 8 Testicular Heat Stress and Sperm Quality 109

Varicocele of testicular cancer. The severity of infertility in human cryptorchidism depends on the position of Varicocele is the most common and treatable the testis, whether one or both of the testis is mal- cause of male infertility and it affects 15 % of the descended, how soon it is surgically corrected male population. It is implicated in 40 % of men and perhaps the underlying pathology [47 ]. In its with primary infertility and in 80 % of men with supra-scrotal position, the testis is hyperthermic. secondary infertility [38 , 39 ]. A varicocele is the This causes heat-induced loss of spermatogonial abnormal tortuosity and dilatation of the testicular differentiation and apoptosis of all germ cells veins in the pampiniform plexus causing retro- (including germ stem cells) as well as an indirect grade blood fl ow in the internal spermatic veins effect of increased oxidative stress and abnormal and venous stasis. Consequently, the cooling of energy metabolism [23 , 48 , 49 ]. In addition, the the testicular arterial blood via the counter current changes in Sertoli cell junctions and abnormal heat exchange becomes ineffective and testicular levels of Leydig cell hormones noted in the crypt- temperature increases towards that of the core orchid testis are linked to hyperthermia [ 50 , 51 ]. body [ 40 ]. Increased scrotal temperature found in Furthermore, despite sperm appearing to be mor- infertile men is most commonly caused by varico- phologically normal [52 ], heat stress produced in cele [ 29, 41]. Both Mieusset et al. [ 29] and conditions of cryptorchidism and varicocele Goldstein and Eid [42 ] reported that infertile men induces sperm DNA fragmentation [52 , 53 ]. with varicocele have higher mean scrotal tempera- tures on (1) the affected testis compared to the unaffected side and (2) both testes compared to Assessing Testicular Temperature that in fertile men. Intra-testicular temperatures in the affected testis were 2.43Ð2.72 ¡C higher than Testicular and intra-scrotal temperatures can be that of a normal testis [42 ]. The underlying mech- measured either directly or indirectly and in the anism of varicocele-related infertility is not clear form of either a single or continuous measurement but is attributable to factors such as increased (Table 8.1 ). Intra-scrotal skin surface temperatures scrotal temperature, oxidative stress, and hor- refl ect the temperature of the underlying testis as monal imbalance [43 ]. Varicocele patients have the testis and epididymis constitute the largest ther- increased apoptosis (programmed cell death) [44 ], mal mass in the hemiscrotum [36 , 54 ]. Testicular and the increase in scrotal temperature (but not temperature may range between 31 and 36 ¡C varicocele grade) is associated with oxidative depending on the method used for the measure- stress-induced apoptosis [43 ]. Chan et al. [45 ] ment of temperature and the presence of any under- found that heat shock proteins 70 and 90 were sig- lying pathology [ 55 ]. Accuracy and reproducibility nifi cantly upregulated in varicocele patients. Heat of the temperature are important as temperature dif- shock proteins are produced in response to various ferences in a normal (euthermic) and pathologic stress inducers including heat, and their increased (hyperthermic) testis may be as small as 0.6Ð1.4 ¡C expression suggest that they play a role in the [ 36 ]. Even these small increases can hamper sper- mechanism of varicocele-related infertility [45 ]. matogenesis and epididymal maturation [36 ].

Cryptorchidism Single or Discontinuous Measurements Cryptorchidism is among the most common con- genital defects in newborns and occurs in 2Ð4 % In this method evolved by Zorgniotti and MacLeod of full-term male births [46 ]. About 50 % of these [36 ], the subject disrobes from the waist below and cases resolve spontaneously within the fi rst year lays supine for about 6 min (to equilibrate to of birth and those that do not resolve naturally an ambient room temperature of about 21Ð23 ¡C) require surgical intervention. Failure of the testis [32 , 36 ]. A mercury thermometer is pre-warmed by to descend leads to infertility and increased risk placing the bulb of the thermometer in contact with 110 D. Durairajanayagam et al. ] ] 55 , 108 , 54 , ] 55 , 36 65 , , 54 , 32 55 4 [ Reference(s) [ ammation, and ammation, conditions (e.g., lying down for several minutes) contact with the testis beneath unclothed alter the readings contribute to differences in reading contribute to differences (temperature in the peripheral testis is lower than the mediastinum testis) the antiseptic solution applied during scrotal skin preparation would alter the temperature scrotal skin infl the intrascrotal disease would affect temperature mercury column is constricted 3. Reproducible only under static 2. Depth of thermistor placement could 3. Use of anesthesia and evaporation 4. Extremes of ambient temperature, values 1. Small dimensions 1. May be displaced from the site of 2. Provides accurate measurements 3. Gives repeatable and standardized 2. Applicable only when subject is 2. Light weigh 3. Assessment done in a clothed state 2. Minor movements of the scrotum could 1. Simple and inexpensive 1. Clinical thermometer unsuitable as its nger the anterior testis using an adhesive against the scrotum thermometer bulb using the thumb and index fi waistband over the most prominent part of anterior testis 1. Attached to the scrotal skin overlying 2. Thermometer bulb held longitudinally 3. Loose scrotal skin drawn around the 2. Electrode cables secured at trouser 1. Placed within the scrotum or testis 1. Direct measurement 1. Invasive procedure [ Description Advantage Disadvantage Methods of measuring scrotal (testicular) temperature in humans Methods of measuring scrotal (testicular) temperature in humans Skin surface thermocouples Thermal resistor (thermistor) needles Table Table 8.1 Method Single measurement or discontinuous method Mercury thermometer 1. Pre-warmed bulb positioned directly 8 Testicular Heat Stress and Sperm Quality 111 ] 110 , ] ] ] 109 109 58 55 , ] , Ð , 55 55 55 56 54 [ [ [ [ [ needs to be calibrated using a black body prior to use emissivity could affect readings emissivity could affect measured and not deep scrotal temperature in temperature differences for research as the comparison with grey scale can introduce inaccuracies absolute numbers of ±0.1 ¡C of ±0.1 ¡C 1. these thermometers For better accuracy, 2. thermal radiation or in skin’s Variations 3. Only the surface temperature is 4. Lacks sensitivity to record small 1. Does not provide the required accuracy 2. but not Provides relative differences 3. Unable to obtain a preferred sensitivity 1. Unable to obtain a preferred sensitivity temperature during normal daily activities in different body positions in different on the same area of temperature 2. Representative of testicular 1. Easy way to measure temperature 2. Permits repeated measurement 1. Allows for a dynamic recording over the most prominent part of testis scrotal skin attached to a belt scrotal skin infrared thermometer with an accuracy of ±0.1 ¡C was preferred crystals the each scrotum using transparent tape 3. Replicate readings taken at the skin 2. Connected to a portable data recorder 2. Connected to a light-weight data logger 2. pistol-type, non-contact, digital A sensitive 1. Measured using temperature- 1. Attached to skin on the anterior face of Thermistor 1. Thermistor attached to underwear Thermography 1. Measured heat emitted from the Infrared thermometry 1. Measures heat emitted from the Liquid crystal thermometry Continuous measurement method Thermoport thermocouples or thermoprobes 112 D. Durairajanayagam et al. a light source or immersing it in warm water, allow- Posture ing the mercury column in the thermometer to expand to a temperature that is slightly higher than Changes in posture affect testicular tempera- the estimated temperature of the testis (i.e., around ture. Scrotal temperature is lowest when stand- 37 ¡C). The thermometer is then quickly positioned ing disrobed [36 , 59 ]. Heat dissipation can directly over the most prominent part of the ante- occur unhindered from the unsupported testis rior testis and the bulb is held longitudinally against when the body is unclothed and in an upright the scrotum. The loose scrotal skin is drawn around position. When comparing body positions, the thermometer bulb using the thumb and index scrotal temperature in the supine or seated posi- fi nger (to include the immersion mark, if present). tion is higher than that in the standing position The mercury column will begin to drop until it [ 32 , 36 , 58 , 59 ]. When walking (upright and reaches equilibrium (usually about 8 s). The read- moving), scrotal temperatures are 0.3Ð1 ¡C ing at that point plus 0.1 ¡C represents the intra- lower than those generated when sitting regard- scrotal temperature [36 ]. The process is then less of clothing type [32 , 59 ]. Scrotal tempera- repeated in the contralateral testis. This method tures are highest during sleep when the body is was modifi ed from the “invagination method” by supine and movement is minimized [32 , 58 , 60 ] Brindley [32 ] and allows for repeatable and consis- compared to other body positions. When com- tent values to be obtained for use in a clinical evalu- paring sleepwear, scrotal temperatures were the ation of, for example, a varicocele [56 ]. lowest when sleeping in the nude compared to sleeping in pyjamas or underwear [32 ]. When in a supine position, the testes are resting on the Continuous Measurements thighs and are in direct contact (conduction) with the relatively higher body temperature. During continuous measurement, two cutaneous Additional layers of clothing trap air and con- thermocouples (thermoprobes) are attached to serve heat. Using an electric blanket or quilt on the skin on the anterior face of the each scrotum top of typical nightclothes while lying down in using transparent tape, and these are connected to bed after a hot bath will give a cumulative effect a small portable data recorder attached to a belt. that is likely to lead to genital heat stress. When Temperatures are recorded at 2-min intervals. assessing diurnal variation, Hjollund et al. [ 56 ] Measurements recorded in the data recorder are found that scrotal temperatures, when measured downloaded to a computer through a specifi c pro- at a 5-min interval for a continuous 24 h, were gram [57 ]. The use of a portable data recorder for higher at night by 1.2 ¡C compared to those continuous determination of scrotal temperature during the day. allows for a dynamic recording of temperature [58 ]. However, scrotal skin temperatures have also Sitting been measured noninvasively for an entire day The length of time spent in a seated position, using a thermistor attached to underwear that is either due to occupational nature, long commutes connected to a light-weight data logger [56 ]. and sedentary leisure activities, also contributes to testicular heat stress. A predominantly seden- tary (sitting) position at work has been shown to Risk Factors for Scrotal increase scrotal temperatures [30 , 56 , 57 ]. When Hyperthermia sitting, the testes are trapped between the thighs. Moreover, the normal seated position leads to The temperature difference between the body and poor ventilation in the groin area, which contrib- scrotum can be affected by a variety of external utes to an increase in scrotal temperature. The thermogenic factors including body posture or positioning of the legs while sitting (i.e., legs position, clothing, obesity, lifestyle and occupa- together, apart or crossed) impacts the scrotal tional exposure, and ambient seasonal tempera- temperature in both the disrobed [59 ] and clothed ture changes (Fig. 8.2 ). state [32 , 57 ]. 8 Testicular Heat Stress and Sperm Quality 113

Fig. 8.2 Various lifestyle, occupational, postural, and environmental factors contributing to testicular heat stress

Paraplegic men in wheelchairs who remain which then results in lower scrotal temperatures, seated for extended periods with closed and unmov- compared to when being seated in a sedentary ing legs were found to have higher deep scrotal manner. temperature and poor sperm motility than normal In a study comparing the increase in scrotal men who were seated freely for 20 min or more temperatures while seated on different types of (without the position of their thighs being specifi ed, chairs, Koskelo et al. [62 ] reported a 3 ¡C increase i.e., kept close together or apart) [32 ]. However, in scrotal temperature upon 20 min of sitting on a when compared in a supine position, there was conventional cushioned offi ce chair. However, no signifi cant difference in scrotal temperatures they found no difference in temperature when between the paraplegic and normal men [32 ]. subjects sat in a saddle chair. This is probably due The insulating effect of the seated posture is to the open hip and knee angles, which allow for compounded by being sedentary but counter- adequate scrotal ventilation [62 ]. Similarly, sit- acted by physical activity. The average scrotal ting with crossed legs causes a bigger increase in temperature in healthy volunteers while sitting scrotal temperature than sitting with the legs on a conventional chair for a period longer than apart (at an angle of about 70¡) [ 63 ]. After 35 min is 36.4 ¡C compared to 34.5 ¡C during remaining in a seated position with crossed legs walking [61 ]. Increased limb movement during for 15 min, the thermogenic effect caused by this physical activity increases perigenital air circula- position further persisted for a minimum of tion, and this allows for better dissipation of heat, 5 min, even after standing up [63 ]. 114 D. Durairajanayagam et al.

When sitting on surfaces with a higher tem- motility [67 , 68 ]. Another study found that men perature, the increase in scrotal temperature attrib- who wear tight underwear have decreased sperm uted to the seated posture is further compounded count and sperm motility compared to those who by the warmth exuding from the seated surface. In wear loose underwear [69 ]. Conversely, in a a Korean study, Song and Seo [64 ] investigated study involving 97 men presenting for primary the effects of sitting directly on a heated fl oor on infertility (aged between 25 and 52 years), scrotal scrotal temperature among 6 healthy male volun- temperatures did not differ between men who teers in a controlled environmental chamber. They wore boxer shorts and those who wore brief style concluded that the fl oor surface temperature and underwear [12 ]. The authors further reasoned the rate of metabolism while in a sedentary pos- that brief style underwear gives a supportive ture affect scrotal temperature and recommended effect that pushes the testes closer to the body that surface temperature of a heated fl oor be main- while the boxer shorts lacks this effect. However, tained within 23Ð33 ¡C to avoid impairment of any additional layer of clothing that is worn over spermatogenesis [64 ]. the underwear (e.g., trousers) would result in the same supportive effect on the testes [12 ].

Clothing Diapers The use of disposable plastic-lined diapers is Irrespective of the body position, wearing cloth- more common these days than cotton, reusable ing has an insulating effect that increases scrotal diapers. Even cotton diapers are usually used in temperature. In the standing and supine posi- combination with a plastic lining as a protective tions, clothing increases scrotal temperatures by covering to prevent leakages. The use of plastic 1.5Ð2 ¡C compared to the naked state [63 , 65 ]. In material reduces the skin’s breathability, which men at rest who are lightly clothed, the layer of would lead to a warm and moist perigenital area, air trapped in the space between the skin and thereby contributing to higher scrotal tempera- clothes is on average 3.5 ¡C higher than that of ture. Partsch et al. [ 70] studied 14 neonates (term ambient air (at a temperature of between 21 and aged 0Ð4 weeks) and pre-term with a gestational 32 ¡C) [66 ]. The reduction in air exchange when age of 28Ð36 weeks (postnatal age 14Ð85 days), in a clothed state contributes to the increase in 22 infants (aged 1Ð12 months), and 12 toddlers scrotal skin temperature [63 ]. Clothing that per- (age 13Ð55 months) and reported that young mits better air fl ow would mean that scrotal heat boys wearing disposable plastic-lined nappies could be more easily dissipated, keeping temper- have increased scrotal temperatures compared to atures closer to physiological levels. Kompanje those wearing reusable cotton diapers (without [ 27] suggested that Scottish kilt-wearing possibly protective pants). However, in another study, produced a more ideal physiological scrotal envi- Grove et al. [71 ] found no differences in the scro- ronment, especially since nearly 70 % of men tal temperature profi les of approximately 70 chose to not wear anything underneath their kilt. young boys (aged 3Ð25 months) wearing dispos- In the Asian region, men often wear only a sarong able diapers with a plastic lining compared to when at leisure, which similarly helps in dispers- those wearing reusable cotton diapers covered ing body and environmental heat to keep lower with plastic pants. Only when the cotton diapers testicular temperatures. were used without any plastic covering were scrotal temperatures lower than those in the boys Tight Underwear, Boxers, Jockey Shorts using disposable diapers [70 , 71 ]. That being It is still debated whether the type of underwear said, as cotton diapers are almost always used has a signifi cant impact on testicular temperature along with the plastic pants, it would seem that and hence, male fertility. Studies have reported practically speaking, both the classic and modern that the regular use of tight underwear over a diaper choices did not differ signifi cantly on their period of time leads to a reduction in sperm effect on scrotal temperature. As to whether 8 Testicular Heat Stress and Sperm Quality 115

diapering preferences (and the higher scrotal removal of excess fat in the scrotal and suprapu- temperatures is generates) at a young age could bic region helped improve sperm count, motility, contribute towards a compromised male fertility and morphology in nearly 65 % of infertile potential as an adult, Jung and Schuppe [72 ] rea- patients, and nearly 20 % of these patients went soned that pachytene spermatocytes and round on to initiate a pregnancy [77 ]. spermatids (the most temperature-sensitive tes- ticular cells) [10 ] are not yet present in the age Sauna group when most children use diapers. The Saunas are a popular method of relaxation and authors concluded that there was no convincing detoxifi cation or cleansing in many parts of the evidence linking genital heat stress with poor world. Temperatures in saunas typically range semen quality in their adulthood [72 ]. between 80 and 100 ¡C at the level of the bather’s head, with humidity ranging from 40 to 60 g of water/kg dry air [78 ]. Conventional saunas pro- Lifestyle vide wet heat through warmed, humid air (radia- tion and convection) as well as warmed surfaces Obesity (radiation and conduction), while modern saunas Obesity is a common lifestyle-related societal such as infrared saunas provide dry, radiant heat. problem of the modern era. Many adults who are Brown-Woodman et al. [79 ] examined the in the reproductive age group have a higher than effect of a single sauna exposure (85 ¡C for normal body mass index (BMI, normal range: 20 min) on sperm parameters at 10 weeks post- 18.0Ð24.9). In fact, the rate of obesity is higher in exposure compared to 3 weeks preexposure. infertile men than in men with normal semen They found that this one acute testicular heat parameters [73 ]. A BMI ≥25 is associated with stress episode was suffi cient to cause the sperm an average 25 % reduction in sperm count and count to reduce within a week post-exposure, motility [74 ]. Obesity is often associated with only to normalize in the fi fth-week post-exposure decreased physical activity and prolonged peri- [79 ]. In a study that continuously (i.e., every 5 s) ods of sitting or being sedentary, which have been monitored scrotal temperature during a sauna found to increase testicular temperatures and con- exposure (87.6 ± 1.3 ¡C and <15 % humidity), sequently suppress sperm production [75 ]. Obese scrotal temperatures were found to reach core males are more likely to have increased fat depo- body temperature within about 10 min of expo- sition in the abdomen and upper thighs and larger sure to the exogenous heat [58 ]. Saikhun’s group waist and hip circumferences. Additionally, scro- assessed the effects of sauna exposure on sperm tal lipomatosis (deposition of fat around the sper- parameters after a 2-week sauna exposure matic cord) in obese men could inhibit (at 80Ð90 ¡C for 30 min) [ 35]. They found that spermatogenesis by several means, i.e., (1) pro- sperm movement characteristics had declined but vide insulation that could disrupt the radiation of were restored within a week after concluding the testicular heat, (2) compress blood vessels, lead- sauna exposure. They reported that sperm param- ing to testicular congestion (venous stasis) and eters such as semen volume, sperm count, num- impaired heat exchange, (3) compress the testicu- ber of motile and morphologically normal sperm lar artery leading to ischemia of the testis, (4) as well as sperm penetration levels had remained hamper the cord’s ability to reposition the testes unchanged [35 ]. More recently, Garolla et al. in response to temperature changes, and (5) dis- [ 80 ] investigated the effects of biweekly Finnish rupt local thermoregulation due to excess fat in (dry) sauna sessions (89Ð90 ¡C for 15 min) for the suprapubic region [76 , 77 ]. The compromised 3 months on ten normozoospermic men. They effi ciency of testicular thermoregulation may found that these frequent sauna exposures (that well lead to elevated testicular temperatures. lasted long enough to cover an entire spermato- However, scrotal lipomatosis could also occur in genic cycle) caused a signifi cant reduction in those who are not obese [ 76 ]. In one study, sperm count and progressive motility (although 116 D. Durairajanayagam et al. they were still within normal range) and altered et al. [ 82 ] found that 25 healthy volunteers mitochondrial function, DNA protamination, and (median BMI of 23.2) who wore cotton wool chromatin condensation in the sperm [ 80 ]. clothing while performing moderate cycling However, sperm morphology and viability (median speed of 25.5 km/h, power around 25 W) remained unaffected while heat shock proteins sitting on the saddle of a stationary cycle for (and their regulating heat shock factors) that con- 60 min had mean scrotal temperatures below fer a protective effect were found to be upregu- 35.6 ¡C. Increases in scrotal temperatures did not lated after testicular heating [ 80 ]. These studies differ signifi cantly between the left and right collectively showed that following sauna expo- scrotum and with time [82 ]. sure, the negative impact on spermatogenesis was signifi cant but reversible. Laptop Usage Sheynkin et al. [84 ] demonstrated among 29 Hot Baths healthy volunteers that using a laptop in a lap Other lifestyle habits such as indulging in a relax- position close to the genital area (i.e., a seated ing soak in a hot tub, heated whirlpool, or a warm position with approximated thighs) for an hour bath could negatively impact male fertility. Shefi contributes to a 0.6Ð0.8 ¡C increase in scrotal et al. [81 ] studied the effects of wet heat exposure temperatures compared to a 2.1 ¡C increase in in a group of 11 infertile men (mean age scrotal temperatures in the same sitting position 36.5 years) who practiced whole body immersion without using a working laptop. This increase in in either a hot tub, heated jacuzzi, or warm bath genital heat could be attributed to heat exposure (at temperatures that were higher than that of from laptops that have internal operating temper- body temperature) for more than 30 min weekly atures of more than 70 ¡C and to the seated pos- (mean weekly exposure was 149 min) for longer ture for those 60 min. Although this study did not than 3 months. Comparison of semen parameters examine changes in semen parameters, the in samples analyzed before vs. 3 months after the authors suggested that since scrotal heat impairs discontinuation of the wet hyperthermia, showed spermatogenesis, then laptop usage also likely improvements, mainly in sperm motility [ 81 ]. affects these parameters [84 ]. They concluded that in certain infertile men, refraining from these types of heat exposure could perhaps reverse the detrimental effects of Occupation hyperthermia on their semen quality. Welders: Radiant Heat Cycling Welders are occupationally exposed to intense A regular, moderate exercise regimen bestows radiant heat, toxic metals and their oxides, and numerous health benefi ts. However, certain forms toxic welding fumes during welding. Bonde [ 85 ] of exercise done in the pursuit of fi tness, cycling, reported that 17 manual metal arc alloyed steel for example, may negatively affect male fertility. welders (mean age 35.9 years) with moderate Scrotal temperatures during cycling may be exposure to radiant heat (31.1Ð44.8 ¡C) and with infl uenced by the duration and intensity of the minimal exposure to welding fume toxicants exercise as well as posture [ 82] and clothing. As experienced a reversible decrease in semen qual- a physical activity, cycling improves perigenital ity. The percentage of sperm with normal mor- air circulation, which aids in the dissipation of phology decreased within 6 weeks of exposure to testicular heat [82 ]. At the same time, cycling radiant heat but increased 4 weeks after cessation involves extended periods of being in a seated of exposure [ 85 ]. In another study, 17 welders posture on a saddle seat for the majority of the (mean age 43.8 years) with 1Ð10 years or exercise and wearing a body-fi tting spandex out- more of welding exposure possibly had some fi t, which would contribute an insulating effect adverse effects on sperm motility, morphology on scrotal temperatures, especially in profes- and physiologic function, although they main- sional cyclists [83 ]. However, in their study, Jung tained a normal range of sperm concentration [86 ]. 8 Testicular Heat Stress and Sperm Quality 117

Bakers: Radiant Heat morphology and thereby sperm quality [ 92 ]. Bakers are reported to take longer to initiate a In a study of 402 fertile couples in France, pregnancy than controls, as only 14 % of bakers’ Thonneau et al. [93 ] found that compared to other partners were pregnant within 3 months couples, the time to pregnancy was signifi cantly (compared to 55 % of controls) and 29 % of prolonged for those couples in which the male bakers’ partners were pregnant within 6 months partner remained seated driving in a vehicle for (compared to 74 % of controls) [87 ]. This sug- longer than 3 h daily. gests that the bakers’ occupational exposure to In addition to the effect of prolonged sitting on heat may be a contributory factor to subfertility. a car seat (which in itself causes about a 2 ¡C increase in scrotal temperature) [57 ], the use of a Ceramic Oven Operators: Radiant Heat heated car seat for longer than 60 min was shown Figà-Talamanca et al. [ 88 ] reported that healthy to cause an increase in scrotal temperature of ceramics oven operators with chronic occupa- 0.5Ð0.6 ¡C, nearing core body temperature [ 94 ]. tional exposure to high temperatures (37 ¡C, 8 h/ This additional factor would likely add towards day) had a higher incidence of abnormal sperm the decline in sperm quality. parameters compared to controls. These individ- uals faced diffi culty in establishing a pregnancy Submariners and had a higher occurrence of not being able to Velez de la Calle [95 ] and co-workers looked into father a child compared to controls [88 ]. the infertility risk factors in a military population from a large military naval base in Brest, France. Professional Drivers They found that male mechanics, cooks, and sub- Long hours of driving and remaining in a seated mariners who were occupationally exposed to position have shown to have detrimental effects very hot working conditions while in the subma- on male reproductive function. The negative rine (temperatures in the rear end of the subma- effect of extended periods of driving on sperm rine close to the motor range between 40 and parameters is attributed to an increase in scrotal 60 ¡C) had sought help for infertility issues. temperature [57 ]. Sas and Szollosi [ 89] investigated the effects of prolonged driving on spermiogenesis in 2,984 Ambient Temperature patients, of whom 281 were occupational drivers. and Seasonality They found that the incidence of abnormal sperm was higher among the patients who drove profes- A 1 ¡C increase in ambient temperature induces sionally and more severe in those with longer a 0.1 ¡C increase in scrotal temperature [32 ]. occupational driving experience. Similarly, In a study of semen samples taken from more workers involved in the transport occupational than 1,000 fertile men from four European cit- group had lower sperm concentrations [90 ] and ies (Copenhagen, Denmark; Paris, France; a higher risk of abnormal sperm motility [91 ] Edinburgh, Scotland; and Turku; Finland), compared to other occupational groups. Figà- Jorgenson’s group found a general seasonal vari- Talamanca et al. [92 ] reported that compared to ation in sperm concentration (summer values control subjects, taxi drivers in the city of Rome were 70 % of winter values) and total sperm had a higher amount of sperm with abnormal count (summer values were 72 % of winter val- morphology and that this was more apparent in ues), but not for sperm motility or morphology the longer-serving drivers. However, sperm con- [ 96]. The difference of approximately 30 % in centration and motility in these drivers ( n = 72) sperm count from winter (highest) to summer were comparable to that of the 50 healthy control (lowest) could be attributed to differences in life- subjects, who were of similar age and had similar style or environmental exposures among the men smoking habits. This study also suggested that [ 96]. Similarly, in a preliminary study of 4,435 prolonged driving time could compromise sperm pre-vasectomy patients, Tjoa et al. [97 ] reported 118 D. Durairajanayagam et al. a circannual rhythm (biological rhythmicity approximating 1 year) in human sperm concen- Scrotal Cooling tration and total sperm count, with a higher sperm count in winter compared to summer. Gyllenborg Several studies have showed that scrotal cooling et al. [98 ] found that sperm counts among a group can improve sperm count, motility, and morphol- of unselected Danish semen donor candidates ogy [103 ]. Devices that have been used for tes- were lowest in the summer although semen vol- ticular cooling include a curved rubber collar ume and sperm motility remained unchanged. fi lled with ice cubes that was taped to both the However, Mallidis et al. [99 ] did not fi nd any thighs for 30 min daily for 14 consecutive days effect of season in semen samples provided by [ 104] and a gel ice pack that solidifi ed upon freez- normal healthy Australian men. ing, which was wrapped in a cloth or towel and inserted in the underwear on the anterior aspect of the scrotum nightly for 2 months—the cooling Mild Scrotal Heating as a Method effect occurred upon the thawing of the ice pack of Contraception within 3Ð4 h [105 ]. Other techniques included a cotton suspensory bandage placed in close con- Scrotal temperatures that are maintained lower tact with the scrotum (worn for 16Ð22 h from 8 to than that of the core body temperature would 20 weeks) that released fl uid (water or alcohol) to help improve spermatogenesis and the fertility maintain a damp scrotum [106 ] and a device potential of men facing infertility issues. attached with a belt to the abdomen and scrotum However, fertile men may fi nd that higher scrotal that released a continuous air stream to achieve temperatures could work in their favor. scrotal cooling nightly for 12 weeks [107 ]. In a Commonly used methods of male contraception study to assess the feasibility of a clinical trial, include hormonal approach, the use of condoms Osman and his group evaluated the use of a non- and vasectomy [100 ]. However, local application greasy hydrogel pad, the Babystart¨ FertilMateª of heat could provide the means for a non- Scrotum Cooling Patch, in patients with mild, hormonal, noninvasive, reversible method of moderate, and severe oligoasthenospermia [103 ]. contraception targeting the testicular level [100 ]. The pad contained 0.5 % w/w natural I-menthol In a preliminary study, Mieusset and Bujan [101 ] and was reported to be more practical and com- induced mild testicular heating (assumed as fortable to use than other cooling devices [103 ]. 1Ð2 ¡C) by immobilizing the testis close to the When the testes were cooled, spermatogenesis inguinal canal daily during waking hours in 9 improved and pregnancy occurred leading to the men aged between 23 and 34 years. These meth- suggestion that hyperthermia played a role in ods did not affect the men’s libido or sexual causing or aggravating male infertility [29 ]. The rhythm, and no pregnancies were reported during factors affecting scrotal (testicular) temperatures the study period [101 ]. Sperm count and motility and their effect on sperm parameters and male normalized within 1Ð1.5 years in all the subjects infertility are summarized in Table 8.2 . involved in this study [101 ]. In another clinical study, Wang et al. [102 ] reported that hot water baths taken in combination with testosterone sup- Conclusion pressed sperm count and motility. Thus, it would seem that mild scrotal heating could potentially Scrotal hyperthermia is a substantial risk factor serve as an alternate contraceptive method. for male infertility. Repetitive transient scrotal However, the endocrine parameters involved in hyperthermia in the current modern lifestyle is regulating spermatogenesis such as the hypotha- likely to have a negative impact upon spermato- lamic and pituitary hormones may well be genesis, specifi cally in men who are of repro- affected by the intentional increase in scrotal ductive age and desire to have children. The temperature. normal healthy male is equipped with local 8 Testicular Heat Stress and Sperm Quality 119 ] ] ] (continued) 32 16 30 Reference(s) No effect on semen parameter No effect No data [ Ð ] No data Ð ] ] ] No data Reduced motility (legs close together) [ , Ð ] No data Ð 59 59 56 66 111 107 ] , Ð , ] Not a risk factor for abnormal semen quality , [ Ð , , 58 57 32 57 32 63 68 61 107 , , ] No data ] , No data , , , Ð , ] No data Ð Ð , , 36 36 63 94 30 56 30 57 59 65 60 61 , , , ] , No data , , , , , , Ð , Ð 32 32 57 62 64 16 30 16 32 32 12 [ [ [ [ [ 58 56 ce oor tting) [ tting) [ Increased (vs. standing or supine) [ Increased (in conventional offi chair—legs narrowly apart) vs. saddle chair—legs wide apart or car seat) temperature (vs. standing or sitting) state) Effects on scrotal/ Effects testicular temperature Reference(s) Impact on sperm parameters and male fertility legs close together or crossed) Lower (when naked vs. clothed or wearing underwear) Increased (vs. standing or supine) Strong correlation between scrotal [ temperatures and duration of sedentary work No difference (vs. loose-fi No difference oor, car seat) oor, Increased (vs. conventional fl tting) Increased (vs. loose-fi Factors affecting scrotal (testicular) temperatures and their effect on sperm parameters and male fertility on sperm parameters and male fertility scrotal (testicular) temperatures and their effect Factors affecting of legs, i.e., crossed, close together or apart) types—cushioned and non- cushioned, plywood and wooden, knee-support, saddle chair) at work) 2. Sitting (regardless of position 4. chair Sitting (on different 5. Sitting (on heated fl 6. Supine (and during night sleep) Increased close to core body Clothing 1. Clothed state 2. Underwear (form-fi Increased (vs. naked or unclothed Table Table 8.2 Exogenous factors contributing to heat stress Posture (physical inactivity) 1. Standing Lower (vs. sitting or supine) [ 3. Sitting (legs apart) Lower (when legs apart vs. when 7. Sitting (sedentary position Posture (physical activity) 8. Moderate walking Lower (vs. sitting) [ 120 D. Durairajanayagam et al. ] 86 ] ] ] ] ] ] , ] ] 75 79 35 80 81 83 85 87 88 [ [ [ Reference(s) cient spermatogenesis but reversible) and lower (but progressive motility (in professional cyclists during competition year) and proportion of sperm with normal morphology reduced Reduced motility, reversible once exposure is discontinued Reduced motility, No change in sperm morphology and viability protamination and nuclear condensation Altered DNA Increased expression of genes associated with hypoxia and heat stress (up-regulation of shock proteins and their regulating heat shock factors) ] ] No data Suppressed sperm production ] [ Reduced sperm motility Ð [ 71 77 81 ] , No data , ] ] ] Reduced sperm count within a week No change in semen volume, sperm count, morphology Reduced sperm count (less effi [ , ] [ ] Sperm density and morphology unaffected Ð No data Ð 71 70 76 58 35 80 68 72 84 [ [ [ Higher (vs. reusable cloth diapers without plastic covering) Effects on scrotal/ Effects testicular temperature diapers with plastic covering) Reference(s) Impact on sperm parameters and male fertility Increased to core body temperature [ Increased to core body temperature [ (maximum value reached is above physiological range) No data Ð Longer time to pregnancy [ (continued) radiant heat Lifestyle 1. Obesity Increased Occupational exposure 1. heat Welders—radiant [ No data Ð concentration, on sperm count, motility, Adverse effects Table 8.2 Table Exogenous factors contributing to heat stress 3. Diapers (disposable) (vs. reusable cloth No difference 2. Sauna Increased to core body temperature [ 3. Hot baths 4. Exercise—moderate cycling Lowered during cycling 5. Laptop usage in lap position Increased 2. Bakers—radiant heat Increased 3. Ceramic oven operators— No data [ [ Ð Longer time to pregnancy [ 8 Testicular Heat Stress and Sperm Quality 121 ] , ] ] 93 , , ] ] ] ] 107 114 115 92 98 53 53 101 37 Ð , , , ] , ] , , , , , 89 95 97 99 11 52 52 29 29 Reference(s) [ 113 104 111 [ [ Improved semen quality Improved sperm density and motility No pregnancy established during exposure period higher risk of lowered sperm motility Higher sperm count in winter if fever occurs during spermiogenesis and motility affected fragmentation Induces sperm DNA Reduced sperm count and percentage of motile and sperm with normal morphology Improved spermatogenesis [ ] fragmentation Induces sperm DNA [ , 63 , , ] Lower sperm output [ 107 ] 58 101 Ð , 112 , , 114 36 59 104 , ] ] ] No data No data , 36 , , Ð Ð , 32 63 29 3 29 29 113 111 No effect [ Effects on scrotal/ Effects testicular temperature Reference(s) Impact on sperm parameters and male fertility No data No data Ð Increased infertility issues Ð No effect [ [ nuclear-powered submarine nuclear-powered 2. Seasonal changes No data Ð Circannual rhythm in sperm count [ 2. Scrotal cooling Decreased [ 2. Varicocele Increased [ Exogenous factors contributing to heat stress 4. Professional drivers No data Ð Lower percentage of sperm with normal morphology, 5. Submariners in a Temperature variations 1. Ambient temperature Increased Exogenous factors contributing to heat stress Pathological conditions 1. Febrile episode 3. Cryptorchidism Exogenous application or removal of heat Ð 1. [ Mild scrotal heating Increased Increased Ð [ [ Reduced sperm concentration, morphology 122 D. Durairajanayagam et al.

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