Corticosteroids in serum of Rana catesbeiana during development and metamorphosis

Abstract

Radioimmunoassays (RIA) for aldosterone (ALDO), corticosterone (B), and cortisol (F) were used to measure corticosteroids in serum of Rana catesbeiana tadpoles and of young and adult frogs. Because of the uncertain identity of the cortisol-like material in the RIA, it was designated “F.” Serum ALDO was detectable in tadpoles by stage VII and it remained at about 2 ng/ml in most stages until midclimax; then its concentration rose to high levels in froglets and frogs. Serum B appeared later in development (by stage XII) and its concentration increased rapidly to an initial peak at stage XVII. The B concentration increased again after midclimax coincident with the rise in ALDO. After stage XV serum B concentration was about 10 times higher than ALDO in most samples. Serum “F” was detectable by stage V and the concentration rose gradually to stage XIV; then it increased more rapidly until midclimax, whereupon its concentration fell precipitously to reach low levels in froglets and adults. A single injection of ACTH (0.1 IU/tadpole) failed to increase serum ALDO, B, or “F” in premetamorphic larvae, but it caused a significant elevation of the two glucocorticoids in prometamorphic animals. Chronic treatment with ACTH or thyroxine (T 4) increased the serum levels of the three steroids. Treatment with ACTH plus T 4 markedly increased ALDO and B responses to the ACTH but the “F” response was diminished. We interpret the results to indicate that low levels of thyroid hormones (TH) sensitize the interrenal to stimulation by ACTH. Higher levels of TH and/or longer exposure to these hormones further enhance the ALDO and B responses while inhibiting the “F” response. The TH may also alter peripheral metabolism and/or clearance of the steroids to produce the changes which were observed. In either case, our results indicate that TH-induced maturation of the hypothalamo-hypophyseal-interrenal axis contributes to the control of development and metamorphosis in anurans. The pattern of serum B and “F” appears to be related to developmental events, such as hind leg growth and gut and tail regression, but the serum pattern of ALDO did not show any such relationship.