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Home , Circulatory system

204.

IMPLICATION OF THE IN TO MEAT QUALITY R. A. MERKEL MI CH I GAN STATE UN I VERSI TY __--__-__------

The internal equilibria of living, functioning muscle depends primarily upon the circulation. Blood carries and other to the muscles and heat, and other waste products of are transported away from the tissues where they are produced to the , kidneys and skin for renoval from the body. Thus zn adequate and essentially continual blood supply is necessary for the main- tenance of a stable internal equilibrium.

Skeletal muscle has a rather extensive blood supply which is derived from branches of neighboring (Wall, 1960). The aY-teries enter into the rnuscle from the epimysium and traverse along the strands of perimysium, dividing into branches and freely anastomosing with' one another. The finer branches of supply axe oriented transversely to the long axes of the muscle fibers, and from them arise the which course between the fibers in the endomysial ma%rix. The arteries and are contiguous to the point at which the terminal and originate, but subsequently these small vessels arise alternately. This orientation presumably allows the intervening capillaries to run in a relatively direct course from to to expedite rapid removal of metabolites (Clark, 1952) . Capillaries are generally oriented longitudionally between the individual muscle fibers as shown in figure 1.. A fine net- work is formed as the longitudional vessels give rise to frequent trans- verse vessels which surround the intervening muscle fibers. The capil- lay network was first described morphologically in detail almost a century ago (Ranvier, 1874a, 187413; Spalteholz, 1888).

Capillary anastomoses are especially well developed at the sites of the motor end plates (Wilkinson, 1929), a site which is especially active metabolically. Additionally, Ranvier (1874a,b) stated that the cross con- necting vessels in the muscle bed frequently exhibit considerable dilations. These enlargements have been suggested to act as reservoirs for oxygen from which muscle fibers can be supplied during sustained activity and during contraction, a time when capillary circulation is impeded. Such reservoirs have not been confirmed in more recent studies (Romanul, 1964; 1965) however.

Capillary density in skeletal muscle has been shown to be directly proportionate to the metabolic rate, particularly in laboratory animals (Krogh 1919a, 1919b; Stoel1925-26; Duyff and Bouman, 1927; Paff, 1930; Martin --et al., 1932; Schmidt-Nielsen and Pennycuik, 1961). However varia- tion in capillary density does exist between muscles within the same species. Also the relationship of capillary density to metabolic rate does not apply unequivocally to the larger domestic animals used for meat production. In fact the pig has a higher metabolic rate than either sheep or cattle, but possesses a similar or slightly lower muscle capillary density than either of these two species (Schmidt-Nielsen and Pennycuik, 1961) . ___-______This manuscript is published with the approval of the Director of the Michigan Agricultural Experiment Station. 205. Capillary density is higher in red muscles than in white muscles (Ranvier, 187La, 187413; Krogh, 1919; Stoel, 1925-26; Smith and Giovacchini, 1956) and in fact the type I or red fibers within a given muscle have greater capillary density than the type I1 or white fibers (Schmidt-Nielsen and Pennycuikj 1961; Rornanul, 1964, 1965; Weatherspoon, 1968) . This distribution of the czpillaries in a cross section of muscle stained for elkaline phosphatase activity results in a positive reaction for sorne as yet unde- termined coriponent of the of small arteries, arterioles ana capillaries. The red muscle fibers are surrounded by approximately twice as many capillaries as white fibers and consequently reference to the capillary: fiber ratio appears in the literature as 2:1 or 1:l fibers (Schmidt-Nj-elsen and Pennycuik, 1961) .

Thus far I have attemlsted to provide a brief description of the capillary bed of skeletal mscle. The previous description and subsequ-ent discussion of the circulatory system is not a cornplete treatise of the subject, but is intentionally restricted to those parameters necessaxy for definition and to those physiological events and characteristics which probably are associated with the ultimate qualitative properties of post-mortem muscle. The role of the vascular bed in normal, functioning muscle --in situ and the possible implications of the circulatory system to post-mortem muscle properties will now be considered. I think it would generally be agreed that data on the relationship of the circulatory system to mdscle quality are essentially non-existent . Thus my remarks will only suggest possible implica- tions of the circulatory system parameters to ultimate post-mortem quality characteristics of muscle. Furthermore, since we, in OUT laboratory, have been studying some aspects of the circulatory system of the pig in an attempt to relate them to muscle quality, I shall subsequently confine most of my discussion to this species.

It is generally conceded that the supply of oxygen to muscle is the most important function of circulation, but whether the delivery of oxygen or the removal of metabolites is more important is not known (Schmidt- Nielsen and Pennycuik, 1961). Oxygen, reversibly bound to , is transported via the capillaies and by the process of p' dsses through the capillary wall, the extracellular fluids and finally through the sarcolemma into the sarcoplasm. The removal of metabolites likewise occurs by diffusion but in the opposite direction or from the muscle cells into the capillary lumen.

An adequate supply of oxygen to skeletal muscle is thus dependent upon a multitude of system; the most obvious of which are: the mbient oxygen , the effectiveness of respiratory exchange within the pulmonary capillaries, the blood flow rate through the muscles, the number and size of the capillaries per c-Jbic unit, the and oxygen binding capacity of the hemoglobin and the oxygen consumption by the muscle cells (Thorling and Ersler, 1968). This complex of systems is integrated by a number of humoral and nervous mechanisms which enable the body to maintain "homeostasisff by counteraction of disequilibria in one system by changes in function of others . Oxygen is a prerequisite for oxidative metabolic activity within the muscle , i.e., type I fibers, and fibers so disposed have a high 206. concentration, a profuse capillary supply or both. The capillary density associated with an individual muscle fiber is not only correlated with the Oxidative activity, but has further meaning in terms of the energy metabolism of the cell (Roxanul, 1965). Skeletd musclp fibers with low oxidative metabolic activity derive their energy from anaerobic glycolysis utilizing as their substrate the intracellular glycogen store (Dawson and Romanul, 1964). Such fibers produce a maximal amount o€ work of short dura- tions and their activity is independent of oxygen supply. These fibers are more or less self-sufficient, depending upon blood supply primarily for the removal of the lactic acid produced and we provided with few capillaries. By contrast, cardiac and skeletal muscle with high oxidative metabolism derive their energy from the aerobic breakdown of a variety of substrates, especially fatty acids. These fibers act for prolonged periods of time and thus cannot depend upon stored substrate, but must obtain it from the circu- lating blood. In addition, the substrate has to be completely metabolized and oxygen is an absolute essential for these reactions. Therefore such fibers depend upon circulating blood for both oxygen and substrate and consequently are surrounded by numerous capillaries. Electron microscopy further reveals that the capillaries on the surface of the fiber are adjacent to the subsarcolemal mitochondrial accumulations -- the sites of the oxidative metabolic activity (Romanul, 1965). From these statements it is readily apparent that the ratio of fiber types and factors that affect oxygen supply to the muscles, particularly the Mediate preslaughter period and during exsanguination, may have profound implications upon post-mortem muscle quality. Let us now consider the possible implications.

Wachtel (1963) compared hemoglobin level, oxygen utilization and of the domestic pig with the European wild pig. The wild pigs had considerably higher hemoglobin levels and blood of the wild pigs was capable of carrying 25-40$ more oxygen than that of the domestic pig of the same body . He also reported that oxygen utilization in wild pigs is lower (34%) than the domestic pig (44%). ordinarily meet increased oxygen demand with an increase in cardiac output. When this is insufficient to met bodily requirements, oxygen utilization increases. Wachtel (1963) states that under resting conditions cardiac output in domestic pigs is already relatively high. This might account for his observation that under conditions of increased oxygen demand, oxygen utilization is greatly increased but cardiac output is only moderately increased in domestic pigs. In wild pigs under similar conditions, cardiac output increases most markedly, while change in oxygen utilization is relatively less pronounced.

Time and pressure events in the of domestic pigs differ quantitatively from other farm animals. They possess less ventricular con- traction and a shorter , the combination of which markedly affects blood flow. In addition domestic pigs have lower blood volumes and a far lower oxygen carrying capacity in the blood than wild pigs. In contrast to wild pigs, the domestic pig is also unable to increase or hemoglobin content during . It has also been reported that the heart of wild pigs contains smaller diameter fibers but considerably more fibers than domestic pigs (Hoernicke, 1966). Heart weight expressed as a percentage of total body weight in the domestic pig is significantly lower than that of other domestic animals and man, and is also lower than wild pigs (Engelhardt, 1966). Additionally the - the of blood oxygenation and removal of venous carbon dioxide - is smaller in domestic pigs than comparable weight wild pigs (Semmler, 1913). 207. From these data it is indeed tenpting to speculate that the cmdio- vascular systeri of the domestlc pi(; is constantly overstrained. The logical question is: how efficiently does thc relatively small heart and lung o€ domestic pigs perfor:? the fuxtions norlraliy reqiired of them? Spoerri (1954) stated that, "It seem 3s if the heart of the domestic pig is able to perform its function effortlessly only ddripg sleep." Thus Lt is rcasonablc to conclud? that the snail heart, low blood volume, frequently low hemoglobin level and pcssible low skeletal nuscle capillary Censity are important factors responsible for a deficient circulatory system in domestic swine. To further augnent this deficiency, it should be recalled that pig muscles have lower myoglobin than the o;hcr meat producing anirids except for ihe very young bovine (Lawrie, 1953a, 1953b, 19662; Bray --et al., 1359; Wilson et al., 1953; Forrest et 1964; T~pdct Thus porcine ckelctz a --al., al., 1966). riusclcc- arc less well adapted to aerobic metabolism than other domesticated meat producing mimals. The possible implications of these stwtline facts to ulti-nate neat quality are obviously many, but let us nOFJ consider some of the more readily apparent 2ossibilities since timE will not permit a morc complete review.

Pigs are extrerzely sensitive to surroundings and they display excessive excitability from such "stressors" as disturbances and fear, by rapid increases in (Engelharat et al., 1961; Wachtel, 1962, 1965; Wachtel --et d.., 1963). Such disturbances elicit a sequence of events which me slmilar irrespective of the nature of the "stressor", notably the release of adrenal nedullary horrnones, epinephrine and norepinephrine folllowcd by the adrenal eorticol 17-hydroxycorticosterone and ll-deoxycorti- costerone (Selye, 1936) . These discharged hormones educe numerous responses in the animal which collectively are referred to as the "genera3 adaptation syndrome" described by Selye. It is not the purpose here to discuss the details of this complex syndrome, but to merely describe in general terms the effect of upon skeletal muscle of the pig.

The initial adrenergic response to any stress releases the medullary catecholamines which can have a precipitous effect 'zpon the efficacy of thc circulatory system via its response on vascular smooth rnuscle in the skeletal muscle bed. causes a decrease in capillary blood flow rate, per unit of time, through the musclature thus decreasing oxygen supply and removal of waste metabolites. Thus, the more efficient aerobic system of chemical energy production in the muscle is impeded and depending upon the severity and duration of the stress condition, the muscle obtains a proportionate amount of its energy for the increased metabolic activity from anaerobic glycolysis. Muscle ATP is rapidly dephosphorylated and oxygen supply exhausted during the violent stress associated with the movement of pigs to slaughter as a result of the captme, restraint and dis- turbances of the slaughter process itself. The ATP is replenished by the anaerobic degradation of glycogen. The product of anaerobic glycolysis, kctic acid, is rapidly produced durirg severe or sdstained stress and because of inefficient removal from muscle by the red-xed capillary circulation, it accumulates, resulting in anoxic .

It has been reported that during anoxic hmoxia an excess of lactate relative to pyruvate is produced. This excess lactate fornation is initiated when arterial oxygen saturation falls below 65% of the normCL vjl-ae (Huckabee, 195Ba, 1958b). Koehler --et al. (1925) reported that anoxic hypoxiel produced marked acidosis in the pig. In their experinents with the pig they 208. obtained an --in situ pH value as low as 6.7 and the carbon dioxide combining potential was depressed to 9.8 volumes %. They stated that anoxic hypoxia was fundamentally an acidotic process and as soon as oxygen want appeared, acid production ensued with a consequential marked acidosis development. That this sequence of events is relevant to the development of pale, soft, exudative porcine muscle is well documented (Lawrie, 1966a, 196673; Lister et al., 1967; Sair --et al., 1967; Briskey and Lister, 1968; Tope1 --et ELL., -196q. An excellent treatise on the implications of hypoxia in the etiology of PSE muscle of "stress-susceptible" and "stress-resistant" pigs was pre- sented by Briskey and Lister (1968) and I shall not attempt to duplicate that effort. The teleological significance of the skeletal muscle fiber type, as well as the proportion and size of each type, upon the development of PSE muscle has not been unequivically elucidated. However, it seems logical that muscles disposed primarily to more oxidative type metabolism would be most susceptible to anoxic hypoxia. However there may be breed differences in this respect.

If the pig is slaughtered during this hypoxic or acidotic condition, lactic acid continues to accumdate rapidly post-mortem and pH drops while muscle is still high resulting in PSE musclature. This rapid lactic acid production apparently results from the accelerated sarcoplasmic ATPase activity which ensues when pH drops below 6.5. The myofibrillar ATPase which is 10 to 20 times more active under normal --in vivo physiological conditions is strongly inhibited by falling pH (Perry, 1956; Bendall, 1960; Wismer-Pedersen, 1966) and plays no significant part in the chemical and physical changes associated with rigor development.

The physiological actions of epinephrine and norepinephrine are very different. Norepinephrine is solely a vasoconstrictor substance; whereas, epinephrine produces vasoconstrictory effects upon skeletal muscle blood vessels in low concentrations and vasodilatory effects in higher concentra- tions as well as having other important metabolic effects (Guyton, 1966). Thus the degree of the adrenergic response to stress could have pronounced effects upon the circulatory flow rate in muscle. in the muscle bed accompanied by increased which is associated with the adrenergic response would increase flow rate per unit of time and thus reduce the exchange time between the blood capillary and the muscle cell. The Pcoz level of the blood stimulates the respiratory center and during pulmonary exchange could likewise be limited so that the blood would be less saturated with oxygen and contain more waste metabolites. This highly speculative effect of the adrenergic response upon the circulatory system of skeletal muscle could explain why the d-blocking and P - stimulatory drugs studied by Lister --et al. (1967) did not provide complete dimunition of PSE musclature. In resting skeletal muscle under normal "" many capillaries are closed to the circulation (Krogh, 1919, 1929). The density of the open capillaries was found to increase after exercise, narcosis, , and other conditions (Krogh, 1919; Sjostrand, 1934; Lindgren, 1934, 1935; Carrow --et al., 1967). The adrenergic response especially if of sufficient severity, would in all probability open available capillaries to the circula- tion which would reduce blood volume in the capillary bed and at least temporarily slow flow rate. The effects of this development upon post-mortem muscle properties would be similar to that previously described if the animal were slaughtered when flow rate was restricted. 209. In spite of the many reported insuTficiencies of the domestic pigs' circulatory system, they are able to run considerable distances without previous training. The failure to complete longer runs is primarily due to insufficient temperature regulat ior, (Hoernicke , 1966) . Dome st ic pigs exercised at ambient of 25OC had great difficulty completing a 2100 m run. However, at -5' and -15% they ran 3000 YI within 30-34 min. The rectal temperature increased steadily to 42.3% at 25OC but stabilized at 40-40.3OC at the lower ambient temperatures. Heart and respiratory rate were &so correspondingly lower. These results indicate that the limiting facto-r for sustained activity was increased body temperature. The possibility exists that the accelerated metabolic activity during such exercise and the concomitant high ambient temperature, in itself a stressor, elicits the s.m~adrenergic sequence of events previously discussed. The ersuing reduced capillary blood flow rate within the skeletal muscle bed apparently is unable to dissipate the heat released by the chemical reactions at a sufficiently rapid rate to keep pace with production and consequently body temperature rises. A relationship between body temperature at the tine of exsanguination and the susceptibility to PSE musclature has been observed (Sybesma and Logtesti jn, 1966; Gahne, 1968; Merkel --et al., 1968). The incidence in PSE development; is markedly increased when body temperature is above 42OC. The mechanism by which the temperature-pH relationship affects the ultimate meat quality has been well documented (Briskey and Wismer-Pedersen, 1961; BendU and Wismer- Pedersen, 1962; Briskey, 1964; Kastenschmidt --et al., 1964; Briskey 7-et al., 1966).

Let us discuss facets of the circulatory system other than capillary bed and its possible implications to meat quality. Nuclear chains, i.e. 6-12 nuclei in a row, found in ventricular muscle fibers of domestic pig heart are considered to be part of an adaptation process. They occur only when muscle fibers are hypertrophied and overstrained, but also appear in the ventricles of wild pigs to a lesser degree (2-4 nuclei in a row). They are not present in cattle or sheep, however (Hoernicke, 1966). It is of academic interest, at least, to speculate that the nuclear chains might be more numerous in the ventricles of stress-susceptible pigs and those which ultimately become PSF, may have a markedly overstrained heart.

Oxygen carrying capacity is determined by red (RBC) number, morphology and state of maturation as well as the hemoglobin level in the RBC. Preliminary work in ow laboratory does not reveal any pathological differences in RBC number, morphology or state of maturation between pigs which have normal or PSE muscle post-mortem (Merkel --et al., 1968). Sybesma and Hat (1965) reported a lower blood volume and higher hematocrit in the Pietrain breed (Highly predisposed to PSE nusclature) than in the Large White and Dutch Landrace breeds (less stress susceptible). Apparently the higher hematocrit is a compensatory response to the lower blood volume; however, since they did not report hemoglobin levels these findings cannot be conclusively evduated.

As previously discussed, domestic pigs have lower hemoglobin levels than wild pigs and thus have 25-40$ less oxygen carrying capacity (Wachtel, 1963). Efforts to increase hemoglobin level in pigs by exercise or administration have not produced any significant increases (Henry c-et al., 1961; Hoernicke, 1966; Charpentier, 1966; Merkel et al., 1968). Thus there 210. appears to be a physiological control over blood hemoglobin level which evidently is entirely adequate under normal conditions, but becomes drasti- cally inadequate when subjected to stress conditions. This observation is further argument for carefill handling of hogs especially just prior to and during slaughter.

In an attempt to corroborate the implication of capillary density in the skeletal muscle bed to ultimate muscle quality we have employed a comb_ination of histological and histochemical techniques (Weatherspoon, 1968) in our laboratory to study this problem. Ham muscles of 3 breeds of pigs (Poland China, Landrace and Chester White) were infused with India ink to study capillary density and the relationship of density to relative area of type I and I1 fibers. The abdominal was cannulated just anterior to the femoral bifurcation. The left femoral artery was ligated to prevent infusion into the left ham muscles. Physiological saline was infused for about 2 min at 160 mm Hg to flush the blood from the capillaries through the severed in- ferior vena cava. A 1:l (v/v) of India ink to distilled at pH 8.6-9.0 was then infused into the muscles of the right ham for about 2 min at 160 mm Hg. The entire in'ected ham was fixed in 10% formalin for 48 hr. A sample approximately 1 cmi in size was removed from the approximate geometric center of the gluteus medius, rectus femoris and semimembranosus muscles, embedded in paraffin sectioned at 10Gthickness and stained with eosin.

The corresponding muscles of the left ham were sampled at approxi- 3 mately the same anatomical position at 0 hr post-mortem. Approximately lcm muscle samples were frozen in liquid nitrogen, sectioned in a cryostat at 12-2Oaand stained for succinic dehydrogenase activity (procedure described by Nachlas --et al., 1957) to identify fiber type. Diffusional geometry is dependent upon capillary density and area of the muscle fibers (Krogh, 1919, 1929; Schmidt-Nielsen and Pennycuik, 1961). The selection for muscling in pigs has undoubtedly resulted in increased growth activity and hypertrophic musclature (Baird, 1952; Ludvigsen, 1954; Wismer-Pedersen, 1968) . Additionally, confinement management systems of swine production have reduced the activity and exercise of pigs. Thus the capillary density per unit area of muscle fibers associated with this relative inactivity and concomitant hypertrophy may be entirely adequate under normal conditions, but is limiting during periods of increased activity.

Thus the capillary density relative to fiber number and particularly area may have important implications. In addition, capillary density asso- ciated with fiber types may also be a contributing factor to muscle quality post-mortem. The application of the infusion technique to porcine musclature 1s illustrated in figures 2, 3, and 4.

In summary the above statements indicate that the domestication of swine has markedly altered the circulatory system. In lieu of the relatively small he& and lung in the domestic pig, the advisability of continued selec- tion for ham and loin muscling without regard for chest capacity is seriously questioned. One wonders if the pig is anatomically and physiologically pre- disposed to circulatory insufficiency. Is this insufficiency characteristic of the pig family or a consequence of domestication? Why do only some pigs 211. develop PSE msclature if circdatory insufficiency is a result of domestice- tion and involved in the etiology of PSE muscle? Other pertinent questions in the implications to PSE developnient are: What are the total synergistic responses of the clrcul&ory and endocrine systems and what do they individually and collectively contribute ta this problem? What is the physiological signif- icance of open capillaries to total capillary densizy ratio? Do closed capll- laries become active during the perids of stress? What is the significance of capillary derisity in relztionship $0 muscle fiber type and to the nunber and area of each type? How does the profile of the glycolytic enzymes and their activities and rate limiting reactions r?late to the circulatory system impli- cations of this problerr.?

These and many other questions are pertinent end znswers to then are necessary before the precise inplications of the circulatory system and its varied parameters to ultimate meat qlality can be objectively defined. As indicated in my openlng remarks, the internal equilibria of xeletai muscle depends primarily upon the blood circulation. ThAs, the magnitude and direc- tion of disequilibria of the circulatory system clt the time of slaughter probably has a mxh more pronounced effect upon post-morterr- qality of meat than any of the other systems.

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Figure 1 A diagrammatic illustration of the longitudinal and transverse orientation of capillaries in skeletal muscle. 215.

Figure 2 A photomicrograph of porcine gluteus medius muscle showing type I (dark) and type I1 (light) fibers stained for succinic dehydrogenase activity. Dark subsarcolemal areas in type I fibers indicate mitochondrial accumulations.

Figure 3 A photomicrograph of porcine rectus femoris muscle showing a higher proportion of type I (~dark)thantype I1 (light) fibers (stained for succinic dehydrogenase activity.) It is readily apparent that when stained for fiber type, mitochondrial accumu- lations as shown in figures 2 and 3 would interfere with capillary identifications. 216.

Figure 4 A photomicrograph of porcine gluteus medius muscle injected with India ink to identify capillaries. Tissues were embedded in paraffin and stained with eosin.

E. J. BRISKEY: We certainly heard three very fine presentations describing the cardiovascular system and some of the variables that tend to possibly influence meat quality. I think they have done a marvelous job, probably eluding some of the problems we are having today and any young aspiring researcher certainly has a lot of things that he could work on if he is so inclined. I think without any more comments, we will open the meeting for any questions that you might want to direct to any one of the three speakers. Please state your name and affiliation before your ques- tions.

MAX JUDGE (I think) : I have a question for Dr. Topel. What do you believe would be the theories behind this and secondly what age do you use?

TOPEL: In regard to the pigs that we are working with, Max? Well, we find the highest incidence of this condition after 180 pounds and we are at the present time conducting a study to determine age influences 217. on gluco-corticoids in the pigs. We are starting at birth, actlally, and going up to 330 pounds. We do not have adequate information to comment on this, but I would say that there is some work being done in Yugoslavia and I have corresponded with therr. They find very high levels of gluco-Corti- coids at birth in the pig and they tend to decrease as the pig matures, so this would kind of fall in line with wh3t we might expect when we observe this condition. I can't give yo-J. an answer, Ma, on why we are getting lower levels of these hormones. In the process of this work Dr. Bd.1 who's working with us riay h;;ve more infornation on this laxer this summer. He is finding some alterztions in the ultra structure of the adrenal glands in these pigs, but I don't think that I cm comment on it at this time. I'm sure in August we can have more information on it.

BOB RUST: I'd like to ask Dr. Merkel--you alluded to the fact thzt the selection for increasing muscle in the ham md loin have reduced the chest capacity and as a result the cardio-vascular capacity of the pTg. Do you have any objective data to support that?

MEXKEL: Well, the work that I reported here--the work of Orinkade and the work of Wattel--pretty well indicates this--that there is a reduced heart size, as well as lung size, in the domestic pig. The fact that we do have hypertrophic muscle in the selection for the meat type hog--1 think this has been fairly well documented--work that was done at Illinois, California, and of course the paper that Dr. William Peterson presented at the Future for Pork Conference--1 think they pretty well doc-ment that. As I say, I think we ought to really seriously question selection for ham and loin per cent or muscling, and of course continue to curtail the chest capacity and its vital organs.

AUTTIS MITLLINS, LSU: I wonder, Bob, if you would comment on the possible adrenergic effect on the state of muscle contraction--you didn't touch upon this at all.

BOB MERKEL: Mo, and I would just as soon not. This is an entire- ly different area.

H. J. TUMA: Dr. Will, Mzybe you would care to comment on that-- you are very familiar with the adrenergic response.

DR. WILL: I don't think that there is really much known on the adrenergic responses in the muscles. It has been alluded to in various ways, but I don't think there is any evidence that can really tell us exactly what is happening, whether it is an adrenergic response per se or whether it is neuro-muscular, which would be different from the effects.

BILL COLE, Tenn.: What actually causes the death of these hogs? ANSWER: Well, from our work that we reported in the field of applied physiology there is definitely a muscular adema which developes, and this of course is manifested in the cardiovascular system or in the myocardium. First, there is in these slides that we showed todsy and in other slides in the illustrations in the article, evidence showing that there is an actual insufficiency of circulatory system or a failure. We 218. reach the point here of a continuing rise in heart rate, even though cardiac output is falling . Pressure has reached its maximum approximately. Heart rate is up near the maximum and the myocardium fails. I think this is what happens in the field cases of these animals--that you have reached the point where the myocardium just cannot keep up. Now this shifts back again to Dave Topel's presentation of the insufficiency of adrenal, but I actually think that the terminal cause of death in this is a circulatory insufficiency or shock.

FERDIE PASSBACH, LSU: Dr. Topel com-nented that potassi-m had some influence along with epinephrine on the cardiovasculaz system. I was wondering if he would care to comment further on this?

TOPEL: Yes, I can. , of course, is intimately associated with adrenal. function, and it is oftentimes found in high levels under stress conditions. What it exactly is doing as far as causing vaso-dilation I don't think we know. It co1,iLd be just a response of excessive metabolism and a shift--1 guess I have to go back one step further. When we have such a low pH in blood--when we have this type of stress syndrome--we have an upset in balance and also in the acid--base balance, and this is when we get into the renal function. You do not have proper secretory levels through the under these conditions, and it is felt that be- cause of the high degree of acidosis, we therefore have a shift from extra- cellular and intracellular characteristics, and this is a direct influence. I don't want to infer that this is causing vaso-dilation itself. I wanted to point out that it is felt that these factors do exist, and these other characteristics, such as probable secretions of the thzt may have a direct effect. These metabolytes are just associations with this characteristic. Does that answer your question?

PASSEACH: Yes. Are these effects only in the renal tubes of the kidney?

TOPEL: As to the reason for the high concentration--you do have a shift from intracellular to extracellular characteristics and this could of course be associated also. But if we had proper function of the kidney, this might be eliminated or might be prevented. So that is the actual function of potassium in this syndrome--in other words it is an inner action and it is rather complicated. The exact mechanism is not known. There are many hypotheses on this however. ##############if