METABOLIC ADAPTATIONS TO FASTING IN HARP SEAL PUPS

Harp seal (Phoca groenlandica) pups were studied during a 32-d postwea ning fast. Body weight was reduced to 63% +/- 0.8% (standard error of the mean [SEM]) of initial value during this period. The plasma level of glucose remained stable at 10.2 +/- 0.3 (SEM) mM, while blood beta- hydroxybutyrate and plasma free fatty acids (FFAs) increased by factor s of 27 and 2.1 from initial levels of 0.06 +/- or (SEM;) mM and 1.44 +/- 0.17 (SEM) mM, respectively. Repeated bolus injections of C-14-ole ate suggested replacement rates of FFAs on the order of 20-29 mu mol.k g(-1). min(-1). The plasma levels of adrenaline, noradrenaline, T-3, a nd T-4 did not change significantly during the fasting period (P > 0.0 5), and plasma cortisol was maintained as low as 143 +0/- 9 (SEM) mM t hroughout the fast. Plasma aldosterone increased from 676 +/- 239 (SEM ) pM on day 2 to 6,821 +/- 2,045 (SEM) pM on day 30 of fasting (P < 0. 01). Daily urine production decreased to only 6% of initial value betw een days 1 and 31, the principal end product, urea, accounting for 90% of excreted nitrogen. The fractional energy release from different ti s sues was estimated from urinary excretion rates of nitrogen and chan ges in body composition determined by computed tomography (CT). It is concluded that about 9% of the energy expended by harp seal pups betwe en days 1 and 3 of the postweaning fast, and less than 4% after day 3, is derived from body protein, the major part of the energy being deri ved from catabolism of fat deposits in the blubber layer and, to some extent, in the core.