Renal function in suckling and fasting pups of the northern elephant seal

Elephant seals fast for prolonged periods without access to water. This is made possible, in part, by reductions in urine production. However, the mec hanisms involved in reducing urine production are not understood. In this s tudy, glomerular filtration rate (GFR) was measured in five northern elepha nt seal pups (Mirounga angustirostris) via the inulin clearance technique. Measurements were made during day 9 and day 18-22 of nursing and the second and eighth week of the postweaning fast. Plasma aldosterone and cortisol c oncentrations, quantified by radioimmunoassay, were measured in eight other weanlings during the second and eighth week of the fast. Mean GFR was 79.3 +/- 29.3 ml/min during the early suckling period and 78.2 +/- 17.1, 89.8 /- 52.7, and 80.4 +/- 12.2 ml/min during the late suckling, early fasting a nd late fasting periods, respectively. Differences between nursing and fast ing were insignificant, possibly because reduced protein oxidation during s uckling and rapid recruitment of protein for tissue synthesis obviated the need for postprandial hyperfiltration. Alternatively, maintenance of GFR du ring fasting may facilitate urea concentration by compensating for reductio ns in the fractional excretion of urea. It is further hypothesized that ald osterone is primarily responsible for mediating renal water reabsorption in this system. (C) 2001 Elsevier Science Inc. All rights reserved.