Serum Relaxin Levels in Young Athletic Men Are Comparable with Those in Women

n the cutting edge Section Editor: Bennie G.P. Lindeque, MD

Serum Relaxin Levels in Young Athletic Men Are Comparable With Those in Women

Jennifer Moriatis Wolf, MD; Kenneth L. Cameron, ATC, PhD; Kari B. Clifton, PhD; Brett D. Owens, MD

and anterior oblique ligament The purpose of this study Abstract: Relaxin was originally described as a reproductive of the basilar thumb joint.5,6 was to evaluate serum relaxin hormone that mediated joint laxity in pregnant women and Relaxin secretion has also in a large population of young has been minimally studied in men. The purpose of this de- been demonstrated in men’s athletic men and to compare se- scriptive laboratory and clinical study was to evaluate serum reproductive tracts.7 Relaxin rum relaxin levels and the pro- relaxin in a young, primarily male population and compare has a key influence on pros- portion with detectable levels levels between the sexes. In addition, the authors evaluated tate growth and development.8 between the sexes. A secondary the relationship between relaxin and generalized laxity. Relaxin receptors have also objective was to evaluate the been shown in the ACLs of relationship between relaxin men, although less consistently and generalized joint laxity. elaxin is a peptide hor- to have multiple physiologic than in women.9 In a study of 9 Rmone that was first de- effects in humans, including men and 5 women (mean age, Materials and Methods scribed as a reproductive improvement of cardiac and 58 years) with congestive heart For this descriptive labora- hormone produced in preg- renal blood flow through va- failure, serum relaxin levels tory and clinical study, the au- nancy, which acts to loosen sodilation3 and prevention of averaged 20 pg/mL, which was thors obtained serum samples pelvic ligaments and soften lung fibrosis.4 In the muscu- approximately 12-fold lower in that were derived from blood the cervix in preparation for loskeletal system, relaxin’s age-matched controls.10 collected for administrative parturition.1 Relaxin is also role in ligamentous laxity has Although normative levels testing during the admissions produced in nonpregnant been investigated in the ante- of relaxin have been inves- process for a military acade- women2 and has been shown rior cruciate ligament (ACL) tigated in pregnant and non- my. Inclusion criteria included pregnant women,2,11 limited age 18 years or older and will- data exist on normative serum ingness to participate by sign- The authors are from the Department of Orthopaedic Surgery (JMW, relaxin levels in men. The ma- ing informed consent. Military KBC), University of Connecticut Health Center, Farmington, Connecticut; jority of reported serum re- cadets are chosen through a and the John A. Feagin Jr Sports Medicine Fellowship (KLC, BDO), Keller Army Hospital, United States Military Academy, West Point, New York. laxin levels in men are derived rigorous screening process The authors have no relevant financial relationships to disclose. from studies of patients with that emphasizes academic ex- This study was supported by a Prospective Research Grant from the renal or cardiac failure and cellence, physical fitness and Orthopaedic Research and Education Foundation (BDO) and pilot funding may be reflective of the effect endurance, and the desire to from the Connecticut Institute of Clinical and Translational Science (Clinical Research Center Grant #M01RR006192) (JMW). of chronic disease on this mul- ultimately serve in the mili- The authors thank Pamela Fall, PhD, of the General Clinical Research tidimensional hormone. No tary. On entrance, they under- Center for her assistance with this project. studies to date have evaluated go extensive physical, mental, Correspondence should be addressed to: Jennifer Moriatis Wolf, MD, serum relaxin levels in a co- and academic testing, and the Department of Orthopaedic Surgery, University of Connecticut Health Center, 263 Farmington Ave, Farmington, CT 06030-4037 ([email protected]). hort of young and physically authors obtained serum from doi: 10.3928/01477447-20130122-06 active men. blood drawn during this pro-

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cess. Blood from 857 men and quencies and proportions were 135 women was collected dur- calculated for categorical vari- Table 1 ing the standard intake physi- ables. Because the relaxin val- Participant Demographics cal in the summer of 2006. ues were not normally distrib- In addition, a subset of this uted, median values and inter- Demographic Men Women group was examined during quartile ranges were also calcu- Mean age, y 18.3061.02 18.0860.78 the intake examination using lated. Pearson’s chi-square test Mean height, cm 177.9767.41 164.1666.58 the Beighton-Horan criteria to was used to examine whether a Mean weight, kg 75.1612.56 61.3968.46 determine generalized laxity.12 greater proportion was found a This study was reviewed and of women with detectable se- Race, No. (%) approved by the Keller Army rum relaxin levels compared White 667 (78.19) 99 (73.33) Hospital institutional review with men. Finally, between- Black 33 (3.87) 10 (7.41) board. group differences in serum re- Asian 38 (4.45) 4 (2.96) Levels of human relaxin-2, laxin values between men and Hispanic 62 (7.27) 14 (10.37) the circulating form of re- women were also evaluated Other 53 (6.21) 8 (5.93) laxin, were determined using using the Kruskal-Wallis test. aRace information missing for 4 men. enzyme-linked immunosor- For evaluation of clinical hy- bent assay (ELISA) sandwich permobility testing, Spearman testing (Quantikine Human correlations between Beighton Relaxin-2 Immunoassay; scores and serum relaxin levels P5.218). In this subgroup, able levels set as 0 (R50.04, R&D Systems, Minneapolis, were performed. All statisti- mean relaxin value was 3.01 P5.28). Similar results were Minnesota). All testing was cal analyses were performed pg/mL in men and 3.60 pg/ observed when the associa- performed in accordance with using STATA/SE version 10.1 mL in women (Table 2). The tion between Beighton score the manufacturer’s protocol. software (StataCorp, College proportion of men and women and serum relaxin levels was Assays were performed in Station, Texas). who had detectable serum examined for men and women duplicate. Results were de- relaxin levels was similar. independently. termined from the standard Results Median values were compared curve, extrapolated to 0. The The authors evaluated se- by sex for detectable serum Discussion mean minimum detectable rum relaxin in 857 men and relaxin concentrations, which Relaxin was originally de- dose of this kit is 1 pg/mL 135 women, for a total of 992 were not significantly different scribed as a reproductive hor- (range, 0.26-4.54 pg/mL). samples tested. This study between the groups (x250.001; mone regulating laxity in preg- The authors evaluated the population had an average age df51; P5.978). The Figure nancy but has been shown to primary outcome of interest— of 18.2660.99 years, average provides a box plot comparing play a wider role in physiolog- serum relaxin levels—similar height of 176.0968.70 cm, and serum relaxin levels between ic function outside pregnan- to the methods used by Dragoo average weight of 73.24612.96 men and women among those cy. Based on a study in mice et al.6 First, 0 values were as- kg. Descriptive values by sex with detectable concentrations. where the relaxin gene was signed to all participants who for age, height, weight, and race Clinical joint hypermobil- absent,14 relaxin is believed to had a serum sample available are presented in Table 1. ity testing was performed in regulate collagen turnover and for analysis but had no de- Mean average serum re- 681 participants, including have a protective effect against tectable serum relaxin values laxin level was 0.50 pg/mL 598 men and 83 women. Mean fibrosis in multiple tissues.15 when the sample was analyzed (range, 0-11.54) in men and Beighton score in this subset Previous studies have identi- by ELISA. Subsequently, a 0.75 pg/mL (range, 0-14.06) was 0.35 (range, 0-7), with a fied serum relaxin levels as a similar subgroup analysis was in women (Table 2). These mean score of 0.26 in men and prospective risk factor for sub- performed that included only calculations included 0 values 0.98 in women (P,.001).13 sequent ACL injury in female those participants with detect- in participants in whom circu- The Beighton score did not collegiate athletes.6 The goals able serum relaxin levels, de- lating relaxin was not measur- correlate with serum re- of the current study were to fined as a serum relaxin level able. Relaxin was detectable laxin levels among those investigate whether circulat- of 1 pg/mL or more. Means by ELISA in 16% (141/857) with detectable levels only ing relaxin was measurable in and SDs were calculated for of men and 21% (28/135) (R520.02; P5.82) or for all young men and to compare re- continuous variables, and fre- of women (x251.52; df51; tested subjects with nondetect- laxin levels between the sexes.

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Table 2 Relaxin Values

Percentiles No. of Mean6SD Relaxin Value Variable Participants (Range), pg/mL 10% 25% 50% 75% 90% IQR Men Relaxina 857 0.5061.34 (0.00-11.54) 0.00 0.00 0.00 0.00 2.03 0.00 Detectable relaxinb 141 3.0161.82 (1.03-11.54) 1.25 1.58 2.59 4.01 5.21 2.43 Women Relaxina 135 0.7562.06 (0.00-14.06) 0.00 0.00 0.00 0.00 10.29 0.00 Detectable relaxinb 28 3.6063.21 (1.03-14.06) 1.03 1.47 2.79 4.33 10.29 2.86 Abbreviation: IQR, interquartile range. aAnalysis of serum relaxin measurements in the entire population, including 0 values. bSubgroup analysis for only participants with detectable serum relaxin levels.

able serum relaxin levels was lar and luteal phases.20 In ad- similar. However, the majority dition, oral contraceptive use of relaxin values from ELISA in women may affect relaxin analysis were undetectable in level, but conflicting evidence both groups. This may indicate exists as to whether oral con- that physiologic relaxin values traceptives increase20 or de- are far lower than is detectable crease serum levels.6 Other po- by current technology or that tential effects on serum relaxin relaxin is episodically secreted in men and women include from the reproductive system. chronic disease, which is ex- Although previous studies pected to be minimal to none reported relaxin levels as high in a military cadet population, as 474 pg/mL in nonpregnant or other medications. women using radioimmunoas- The authors were unable say techniques,18 more recent to demonstrate a relation- Figure: Box plot comparing median serum relaxin concentrations and interquartile range by sex among participants with detectable values (P5.978). ELISA techniques have shown ship between serum relaxin lower levels in the current and generalized joint laxity. study and others.6 The serum Other studies have similarly The authors examined se- studies have examined relaxin relaxin levels observed among been unable to draw a direct rum relaxin concentrations in values in women, but the ma- the young, athletic women in correlation between relaxin a young, athletic group of men jority of these have focused on the current study are similar level and measures of joint and women who were entering pregnancy16,17 or are related to to those reported by Dragoo mobility. This may indicate military college. Relaxin was reproduction. et al6; however, the propor- that relaxin indirectly affects detectable in this population No significant difference tion with detectable levels was the ligaments. Whether serum of young athletic men, with a was observed in serum re- higher (35%) in their study.6 relaxin levels are a risk factor mean value of detectable se- laxin levels between men and Some data suggest that re- for ACL and other musculo- rum relaxin of 3.01 pg/mL. women when all samples were laxin levels in women vary skeletal injuries in men has yet To the authors’ knowledge, analyzed or in the subset of overs the menstrual cycle to be evaluated. Faryniarz et this is the first study to report participants who had detect- and are higher in the luteal al9 noted that relaxin receptors reference values for serum re- able levels of serum relaxin. phase.2,19 However, other stud- were present in 4 of 5 female laxin levels in a large group of In addition, the proportion of ies have shown that relaxin is ACL samples compared with 1 young, athletic men. Multiple men and women with detect- detectable in both the follicu- of 5 male ACL samples using

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radioimmunoassay analysis, ries or medications, which may volar oblique ligament. J Hand 14. Samuel CS, Zhao C, Bathgate Surg Am. 2006; 31(1):80-84. RA, et al. The relaxin gene- and other investigators found have affected relaxin levels. 6. Dragoo JL, Castillo TN, Braun knockout mouse: a model of Ann N Y no relaxin receptors in the HJ, Ridley BA, Kennedy AC, progressive fibrosis. Acad Sci male ACL tissue.21 Conclusion Golish SR. Prospective corre- . 2005; 1041:173-181. The results of the current The authors noted detect- lation between serum relaxin 15. Samuel CS, Lekgabe ED, concentration and anterior Mookerjee I. The effects of study suggest that no differ- able serum relaxin levels in a cruciate ligament tears among relaxin on extracellular matrix ences exist between men and subset of participants drawn elite collegiate female ath- remodeling in health and fibrot- from a young, athletic military letes. Am J Sports Med. 2011; ic disease. Adv Exp Med Biol. women in either the proportion 39(10):2175-2180. 2007; (612):88-103. with detectable serum relaxin cadet cohort including men 7. Sokol RZ, Wang XS, Lechago 16. Chen J, Qiu Q, Lohstroh PN, levels or in the median serum and women, with nonsignifi- J, Johnston PD, Swerdloff RS. Overstreet JW, Lasley BL. relaxin concentrations. As a cant sex differences. In a sub- Immunohistochemical localiza- Hormonal characteristics in the tion of relaxin in human pros- early luteal phase of conceptive result, it is possible that young, set of two-thirds of this group, tate. J Histochem Cytochem. and nonconceptive menstrual athletic men with detectable the authors found no correla- 1989; 37(8):1253-1255. cycles. J Soc Gynecol Investig. serum relaxin concentrations tion between relaxin level and 8. Samuel CS, Tian H, Zhao L, 2003; 10(1):27-31. may also be at increased risk generalized joint laxity. These Amento EP. Relaxin is a key 17. Haning RV Jr, Canick JA, mediator of prostate growth Goldsmith LT, Shahinian KA, for ACL injury, as has been findings provide support to a and male reproductive tract de- Erinakes NJ, Weiss G. The ef- shown in women,6 as well as broader role for relaxin as a velopment. Lab Invest. 2003; fect of ovulation induction on other ligamentous injuries to hormonal regulator of collagen 83(7):1055-1067. the concentration of maternal 9. Faryniarz DA, Bhargava M, serum relaxin in twin pregnan- the joints; however, further homeostasis rather than simply Am J Obstet Gynecol Lajam C, Attia ET, Hannafin cies. . prospective study is needed a reproductive hormone. JA. Quantitation of estrogen 1996; 174(1 pt 1):227-232. to evaluate this hypothesis. receptors and relaxin bind- 18. Harris-Love ML, Morton ing in human anterior cruciate SM, Perez MA, Cohen LG. Serum relaxin levels have also References ligament fibroblasts.In Vitro Mechanisms of short-term been shown to correlate with 1. Hisaw FL, Zarrow MX. The Cell Dev Biol Anim. 2006; training-induced reaching im- decreased patellar tendon stiff- physiology of relaxin. Vitam 42(7):176-181. provement in severely hemi- Horm. 1950; 8:151-178. 10. Dschietzig T, Richter C, paretic stroke patients: a TMS ness in young women, but this Neurorehabil Neural 2. Bryant GD, Panter ME, Bartsch C, et al. The pregnancy study. Repair has not been studied in men. Stelmasiak T. Immunoreactive hormone relaxin is a player in . 2011; 25(5):398-411. A limitation of this study relaxin in human serum dur- human heart failure. FASEB J. 19. Kelly PJ, Eisman JA, Stuart MC, ing the menstrual cycle. J 2001; 15(12):2187-2195. Pocock NA, Sambrook PN, was the small proportion of Clin Endocrinol Metab. 1975; 11. Bryant GD, Chamley WA. Gwinn TH. Somatomedin-C, participants with detectable 41(06):1065-1069. Plasma relaxin and prolactin physical fitness, and bone den- J Clin Endocrinol Metab relaxin; these numbers may 3. Samuel CS, Hewitson TD. immunoactivities in pregnancy sity. . 1990; 70(3):718-723. not have sufficient power to Relaxin in cardiovascular and and at parturition in the ewe. J renal disease. Kidney Int. 2006; Reprod Fertil. 1976; 48(1):201- 20. Pehrsson M, Westberg L, determine a difference between 69(9):1498-1502. 204. Landen M, Ekman A. Stable se- sexes. Also, the timing of blood 4. Samuel CS, Royce SG, Chen B, 12. Beighton P, Horan F. rum levels of relaxin throughout sampling, which was not linked et al. Relaxin family peptide re- Orthopaedic aspects of the the menstrual cycle: a prelimi- nary comparison of women with to the menstrual cycle in wom- ceptor-1 protects against airway Ehlers-Danlos syndrome. J fibrosis during homeostasis but Bone Joint Surg Br. 1969; premenstrual dysphoria and Arch Womens Ment en, may affect the ability to not against fibrosis associated 51(3):444-453. controls. with chronic allergic airways Health. 2007; 10(4):147-153. detect relaxin levels in women. 13. Cameron KL, Duffey ML, disease. Endocrinology. 2009; DeBerardino TM, Stoneman 21. Dragoo JL, Lee RS, Benhaim An additional limitation is that 150(3):1495-1502. P, Finerman GA, Hame SL. the authors did not have the PD, Jones CJ, Owens BD. 5. Lubahn J, Ivance D, Association of generalized joint Relaxin receptors in the human ability to link serum samples Konieczko E, Cooney T. hypermobility with a history of female anterior cruciate ligament. Am J Sports Med. 2003; to participants’ medical histo- Immunohistochemical detec- glenohumeral joint instability. J tion of relaxin binding to the Athl Train. 2010; 45(3):253-258. 31(4):577-584.

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