Some comparative studies in adrenocortical steroidogenesis: An interpretation of the functional homologies of the mammalian and non-mammalian adrenal cortex

Abstract

Using a technique of incubation with dialysis of products, steroid synthesis by adrenal tissue from the skink, Tiliqua rugosa, and the fresh water teleost Coregonus clupeoides was compared with the rat adrenal z. glomerulosa. [ 14C]-Acetate and [ 3H]-pregnenolone were used as precursors throughout. The preparations showed a number of similar features. 1. 1. In each case, aldosterone and corticosterone were prominent products formed from both precursors. 2. 2. Two pools of steroid products were demonstrated, a free and a bound pool. Typically, [ 14C]-labelled steroids were bound and [ 3H]-products were more freely dialysable. In the rat. z. glomerulosa and the Coregonus incubations, the bound steroid was released by the addition of an appropriate ACTH preparation. 3. 3. The two pools of steroid appeared to have different metabolic fates. The free pool gave rise predominantly to corticosterone in the rat and Tiliqua and generally had a high 3H/ 14C ratio. The bound pool gave rise to aldosterone which had a low 3H/ 14C ratio. In the rat z. glomerulosa and in Coregonus, the release of bound steroid caused by ACTH was associated with a decrease in yields of aldosterone relative to glucocorticoid formed from [ 14C]-acetate. Neither the formation of aldosterone nor the ACTH-sensitive compartmental arrangement of steroid is found in the rat inner adrenocortical zones. In common with other features these findings suggest comparability of non-mammalian adrenocortical function with the mammalian z. glomerulosa.