Abstract
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 declind 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·1−1 to 5–7 mmol·1−1 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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Abbreviations
- AA:
-
amino acid(s)
- AMR:
-
average metabolic rate
- ANOVA:
-
one-way analysis of variance
- BMR:
-
basal metabolic rate
- BUN:
-
blood urea nitrogen
- EP:
-
end product
- EWL:
-
evaporative water loss
- [Gr]s :
-
serum creatinine concentration
- GFR:
-
glomerular filtration rate
- LBM:
-
lean body mass
- LML:
-
Long Marine Laboratory
- MR:
-
metabolic rate
- NEFA:
-
non-esterified fatty acids
- RMR:
-
resting metabolic rate
- TCA:
-
tricarboxylic acid
- U:C:
-
ulinary urea: creatinine concentration ratio
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Adams, S.H., Costa, D.P. Water conservation and protein metabolism in northern elephant seal pups during the postweaning fast. J Comp Physiol B 163, 367–373 (1993). https://doi.org/10.1007/BF00265640
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DOI: https://doi.org/10.1007/BF00265640