Sh. Adams et Dp. Costa, WATER CONSERVATION AND PROTEIN-METABOLISM IN NORTHERN ELEPHANT SEAL PUPS DURING THE POSTWEANING FAST, Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 163(5), 1993, pp. 367-373
Urine production and N output were monitored in northern elephant seal
(Mirounga angustirostris) pups progressing through 10 weeks of a natu
ral postweaning fast. Urine output declind by 84% (to 69 +/- 12 ml . d
ay-1) at 10 weeks (P < 0.05). Glomerular filtration rate at 10 weeks w
as 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 a
n initial 11 mmol . l-1 to 5-7 mmol . l-1 by 5 weeks. The fall in urin
ary N loss (and thus amino acid oxidation) was concomitant with depres
sed metabolic rate. Therefore, protein contributed little toward meeti
ng energy demands (i.e., < 4% of average metabolic rate) throughout fa
sting. These data indicate that fasting pups improve water conservatio
n and minimize protein catabolism during prolonged natural fasts witho
ut an exogenous source of water.