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Water conservation and protein metabolism in northern elephant seal pups during the postweaning fast

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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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