WRIGHT, M.L.*; DUFFY, J.L.; GUERTIN, C.J.; SZATKOWSKI, M.C.: Diurnal profiles of adrenal cortical steroids in the plasma of bullfrog (Rana catesbeiana) tadpoles.

Adrenal cortical steroids may potentiate the action of the thyroid hormones (TH) in metamorphosis. The level of these hormones in bullfrog tadpole plasma has been determined at various metamorphic stages but the diurnal rhythm has not been studied. Plasma corticosterone (CORT), hydrocortisone (HC), and aldosterone (ALDO) were measured over a 24-hr period. In both late prometamorphic and early climax tadpoles, the corticoid rhythms in the plasma varied with the light/dark (LD) cycle. On a given LD cycle HC and ALDO profiles were different from each other at prometamorphosis, and both rhythms changed at climax, when the diurnal profiles of all the steroids became similar. The 24-hr mean, and the highest point on the curves, were compared with results in the literature. CORT, which was only detectable at climax, and ALDO, values compared well with previous work but HC was considerably lower than had been reported. On 18L:6D and 6L:18D, CORT was much higher than ALDO at climax, but these two corticoids were nearly the same on 12L:12D. The results show the importance of conducting measurements of plasma hormones on a defined LD cycle, and of sampling throughout a 24-hr day to obtain accurate estimates of hormone levels at a given point in the life cycle. (Supported by NSF IBN9723858.)