Kinetic aspects of cycloheximide-induced reversal of adrenocorticotropin effects on steroidogenesis and phospholipid metabolism in rat adrenal sections in vitro.

Abstract

We examined the rate of cycloheximide-induced reversal of ACTH effects on steroidogenesis and phospholipid metabolism in adrenal sections in vitro. In the absence of cycloheximide, ACTH treatment elicited sustained increases in steroidogenesis (approximately 3- to 5-fold) and adrenal concentrations (approximately 2-fold) of phosphatidic acid, phosphatidylinositol, and polyphosphoinositides. These increases in phospholipids were not dependent on steroidogenesis, since they were also apparent in aminoglutethimide-blocked adrenal sections. The addition of cycloheximide 30 min after ACTH treatment reversed the stimulatory effects of ACTH on steroidogenesis and phospholipids, and the rates of decay for both processes were identical, viz 28 min. This relatively slow turnover in adrenal sections in vitro contrasts with a much more rapid turnover observed previously in vivo and presently in dispersed adrenal cells in vitro; thus, it appears that an artefact of the in vitro adrenal section system stabilizes the putative labile protein. More importantly, the identical rates of decay for steroidogenesis and phospholipids suggest that the same labile protein is required for both phospholipid metabolism and steroidogenesis. These findings are in keeping with our postulate that the labile protein is required for phospholipid metabolism, which, in turn, is required for steroidogenesis.