In vitro steroidogenesis by the nonzoned adrenocortical tissue of the skink, Tiliqua rugosa.

Steroid formation by adrenocortical tissue from the shink, Tiliqua rugosa, has been studied using established in vitro techniques. Both in conventional incubations, with timed sampling, and in incubations with dialysis, aldosterone, and corticosterone were major products. From endogenous precursors, and from [¹⁴C]acetate, yields of the two products were of the same order, whereas from [³H]pregnenolone maximal yields of corticosterone were at least tenfold greater than aldosterone. Maximal rates of steroid formation from the radioactive precursors occurred within the first few minutes of incubation, but maximal rates of steroid formation from endogenous precursors occurred significantly later, between 1–2 hr.In incubations with dialysis [¹⁴C]aldosterone was significantly less dialysable than [³H]aldosterone under all conditions, whereas [¹⁴C] and [³H]corticosterone were homogeneous. In contrast, neither aldosterone nor corticosterone formed from endogenous precursors were bound under control conditions, although binding was increased following dexamethasone pretreatment, and decreased following stimulation with Tiliqua pituitary extract (but not Synacthen), with concomitant changes in yields and specific activities.Inter alia the results suggest that products formed from [¹⁴C]acetate and from [³H]pregnenolone may be maintained in separate pools within the tissue, and this accounts for their different metabolic fates. The bound pool, penetrated only by [³H]acetate, yields more aldosterone than the free, and may be termed a “biosynthetic pool.” In addition there exists a “secretory reserve pool.” This is suggested by the difference between rates of steroid secretion from endogenous and added precursors, and also from the changes in dialysibility seen in steroids formed from endogenous precursors under different conditions of stimulation.In both the compartmental arrangement of steroids, and the production of large yields of aldosterone the adrenocortical tissue of Tiliqua shows similarities to the zona glomerulosa, but not the inner zones of the rat adrenal cortex.