1986. Metabolic and hormonal correlates of molting and regeneration of pelage in Alaskan harbor and spotted seals (Phoca vitulina and Phoca largha). Can. J . Zool. 64: 1086-1094. Cellular, hormonal, and metabolic changes during annual molts and regeneration of the pelage were studied in two harbor and five spotted seals of different ages. Seals were maintained in an appropriate photoperiod and monitored biweekly to monthly by measuring their serum cortisol, thyroxine, and triiodothyronine and their standardized resting metabolic rate. Concurrently, external signs of their molt (shedding of hair) were recorded, and samples of skin were collected from the midback for histological determination of the duration of the regenerative phase of the pelage cycle. Timing of the molts coincided with those of free-ranging seals in the natural environment. The overall duration of the period of shedding and regeneration, from first descent of the hair bulbs on the face and flippers to full emergence of new hair on the back, was estimated as 120-170 days. During the period of descent of the hair bulbs and initial growth of new hair on the back, the resting metabolic rate declined an average of 18.6% below premolt values, generally reaching its minimum when shedding of the old hair and rapid growth of new hair began. Serum cortisol generally reached a maximum just before or during the main shedding of hair from the torso, then decreased abruptly to its premolt level or lower during the main period of rapid growth of new hair. Although corticosteroids appear to inhibit protein anabolism, they favor fat catabolism and may in this way help to maintain the slow growth of new hair before and during the first part of the molt. Serum concentrations of thyroid hormones declined to minima early in the molt, then increased to maxima toward the end, when growth of new hair was most rapid. ASHWELL-ERICKSON, S., F. H. FAY, R. ELSNER et D. WARTZOK. 1986. Metabolic and hormonal correlates of molting and regeneration of pelage in Alaskan harbor and spotted seals (Phoca vitdina and Phoca largha). Can. J . Zool. 64: 1086-1094. Les changements cellulaires, hormonaux et mktaboliques au cours de la rnue annuelle et du renouvellement du pelage ont fait l'objet d'une Ctude chez des phoques, deux P. vitulina et cinq P. larghu de diffkrents iiges. Les phoques Ctaient gardCs dans un environnement B photophiode appropriCe et des manipulations, a raison de deux par semaine a une par mois, permettaient de mesurer leurs concentrations de cortisol, de thyroxine et de triiodothyronine sCriques et d'Cvaluer leur taux de mCtabolisme au reps.En mCme temps, les manifestations externes de la rnue (perte de poils), Ctaient notkes et des Cchantillons de peau sur le milieu du dos Ctaient prClevCs pour permettre 1'Cvaluation histologique de la durCe de la phase de renouvellement du pelage. La @ride de la rnue coincidait avec celle de phoques libres en nature. La dude totale de la pCriode de perte de poils et de la p6riode de renouvellement du pelagem, c'est-a-dire du pr...

The comparative physiologist chooses from the broad spectrum of animal species those which best demonstrate the phenomenon he wishes to study. Accordingly, investigations into the physiology of asphyxia might logically start with those animals which have a special adaptation to breathholding during prolonged underwater dives. In this article we shall consider some inferences from the comparative physiology of diving by examining the cardiovascular responses to immersion of some aquatic species and comparing them with responses of some terrestrial animals, including man. Apnea, simple cessation of breathing during immersion, is characteristic of diving. It leads to progressively increasing tissue anoxia and hypercapnia, and eventually to asphyxial death. It will be seen that the associated circulatory and cardiac adjustments are so profound as to considerably extend the normal range of physiological responses. Historical Review

Regional blood flow and cardiac output were determined by distribution of radioactive microspheres injected via catheter into the left ventricle during experimental diving and recovery in juvenile spotted seals (Phoca vitulina largha) and grey seals (Halichoerus grypus). Cardiac output was 9.7 L/min before diving, declined 90% during submersion and increased to 12.1 L/min after 40 s of recovery. Left ventricular myocardial perfusion declined from 179 +/- 24 (21) to 25 +/- 2 (6) ml/min . 100 g at 2 min submersion, and measured 23 +/- 3 (8) after 10 min of submersion. Cerebral cortical flow was reduced from a pre-dive value of 115 +/- 3 (15) to 40 +/- 5 (3) and 49 +/- 6 (3) at 2 and 5 min of diving, respectively, but increased to 253 +/- 14 (4) ml/min . 100 g at 10 min along with elevated PCO2 (84 torr) and lowered pH (7.10) in arterial blood. It remained at that level in recovery. Brain stem perfusion after 10 min submersion was still identical with control, but increased to 275% of control in recovery. Adrenal flow decreased to 34 and 27% of control at 2 and 5 min of diving, respectively. Recovery flow after 10 min of diving was 200% of control. Liver, kidney, fat, skin, and stomach were ischemic throughout the dive. Recovery flow increased slowly in these tissues. Skeletal muscle (M. psoas) was perfused at a low rate. (3 ml/min . 100 g) pre-dive and was ischemic during diving. Recovery muscle perfusion was variable at different sites (from 5 to 105 ml/min . 100 g). Pre-dive pulmonary capillary perfusion was 58 +/- 8 (9) ml/min . 100 g, decreased to 7 +/- 0 (3) ml/min . 100 g min of submersion, and had increased to 50% of pre-dive value after 40 s of recovery from a 10 min dive. Conclusions are: (1) previous information from implanted flow transducers was confirmed, (2) detailed data for discrete tissues elaborate the concept of selective redistribution of cardiac output in diving seals, (3) non-uniform reperfusion contributes to the maintenance of arterial pressure during recovery, and (4) substantial A-V shunting of cardiac output took place in the first 2-5 min of the dive, when total capillary/nutritive flow was low. Late in the dive, however, CO was routed through systemic capillaries mainly in the cerebral circulation and less than 15% through A-V shunts.

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While diving, seals are exposed to apnea-induced hypoxemia and repetitive cycles of ischemia/reperfusion. While on land, seals experience sleep apnea, as well as prolonged periods of food and water deprivation. Prolonged fasting, sleep apnea, hypoxemia and ischemia/reperfusion increase oxidant production and oxidative stress in terrestrial mammals. In seals, however, neither prolonged fasting nor apnea-induced hypoxemia or ischemia/reperfusion increase systemic or local oxidative damage. The strategies seals evolved to cope with increased oxidant production are reviewed in the present manuscript. Among these strategies, high antioxidant capacity and the oxidant-mediated activation of hormetic responses against hypoxia and oxidative stress are discussed. In addition to expanding our knowledge of the evolution of antioxidant defenses and adaptive responses to oxidative stress, understanding the mechanisms that allow adapted mammals to avoid oxidative damage has the potential to advance our knowledge of oxidative stress-induced pathologies and to enhance the translative value of biomedical therapies in the long term.

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