Water conservation and protein metabolism in northern elephant seal pups during the postweaning fast.
Urine production and N output were monitored in northern elephant seal (Mirounga angustirostris) pups progressing through 10 weeks of a natural postweaning fast. Urine output declined by 84% (to 69 +/- 12 ml.day-1) at 10 weeks (P < 0.05). Glomerular filtration rate at 10 weeks was 51% of the 67 +/- 3 ml serum.min-1 observed during week 1 (P < 0.05). Urine N excretion fell by 69% to 1.2 +/- 0.17 g.day-1, while urinary concentration increased (P < 0.05). Serum urea declined from an initial 11 mmol.l-1 to 5-7 mmol.l-1 by 5 weeks. The fall in urinary N loss (and thus amino acid oxidation) was concomitant with depressed metabolic rate. Therefore, protein contributed little toward meeting energy demands (i.e., < 4% of average metabolic rate) throughout fasting. These data indicate that fasting pups improve water conservation and minimize protein catabolism during prolonged natural fasts without an exogenous source of water.
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Department of Marine Sciences, University of California, Santa Cruz 95064.
Costa
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D000818:Animals; D003404:Creatinine / Q000652:urine; D004231:Diuresis; D005215:Fasting; D009584:Nitrogen / Q000652:urine; D011506:Proteins / Q000378:metabolism*; D046048:Seals, Earless / Q000378:metabolism* / Q000652:urine; D014508:Urea / Q000652:urine; D014867:Water / Q000378:metabolism*; D014886:Weaning
D011506:Proteins; D014867:Water; D014508:Urea; D003404:Creatinine; D009584:Nitrogen