High corticosteroid levels in plasma of adult and foetal Weddell seals (Leptonychotes weddelli).

Pregnant and non-pregnant Weddell seals and foetuses were found to have very high plasma concentrations of corticosteroids (1--7 mumol/l) that were unaffected by stress. Cortisol comprised most of the corticosteroid in the adult but only 50% of that in the foetus. The affinity constant (4.30-5.53 x 10(7) l/mol) and specificity of CBG and the MCR (4.5 l/d/kg lean body mass) in adult seals were similar to those of Man. The binding capacity of CBG (1.48--1.86 mumol/l) which is approximately three times that of Man contributed to the high plasma corticosteroid concentrations but the main factor was the cortisol turnover rate of 3670 mumol/d (1.3 g/d) which is the highest value reported in any species.