AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 2 267-R272, Copyright © 1991 by American Physiological Society
Adaptations to prolonged fasting in free-living weaned gray seal pups
J. J. Reilly
Sea Mammal Research Unit, Natural Environment Research Council, Cambridge, United Kingdom.
The water and energy metabolism of 12 free-living gray seal pups during
their postweaning fast was investigated using tritiated water for
determination of rates of energy expenditure and water turnover and changes
in body composition. Changes in serum composition and urinary output were
also measured. The duration of the postweaning fast ranged from 10 to
greater than 28 days. The mean daily energy expenditure of pups was 12.0
+/- 1.0 (SE) MJ, equivalent to 2.7 times the basal metabolic rate predicted
from M. Kleiber (The Fire of Life. Huntington, NY: Krieger, 1975). On
average, lipid catabolism provided 94% of the energy used. Water-turnover
rates were lower than predicted from C. R. Richmond, W. H. Langham, and T.
T. Trujillo (J. Cell. Comp. Physiol. 59: 45-55, 1962). Urinary output of
water and solute were also low, and these declined as the fast progressed.
Although pups were in negative water balance, there was no evidence that
they experience dehydration during the post-weaning fast. The principal
adaptations to prolonged fasting in weaned gray seals are, therefore,
lowering of field metabolic and water-turnover rate and reliance on stored
lipid as fuel.
