A23187 Inhibits Adrenal Protein Synthesis and the Effects of Adrenocorticotropin (ACTH) on Steroidogenesis and Phospholipid Metabolism in Rat Adrenal Cells in Vitro: Further Evidence Implicating Phospholipids in the Steroidogenic Action of ACTH*

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Abstract
We examined the effects of ACTH and the Ca++ ionophore, A23187, on steroidogenesis and phospholipid metabolism during incubation of dispersed rat adrenal cells. Increasing doses of ACTH elicited nearly parallel increases in corticosterone production and adrenal inositide (mono- and di-) concentrations. As reported previously by other investigators in Y1 cells, A23187 inhibited ACTH- and cAMP-stimulated, but not basal or pregnenolone-stimulated, corticosterone production. A23187 also inhibited ACTH-induced increases in phosphatidic acid, phosphatidylinositol, and diphosphoinositide, and this was attended by inhibition of [3H]leucine incorporation into protein. These findings support our previous contentions that: 1) a labile protein is required for ACTH-induced increases in adrenal phospholipids in the phosphatidate-polyphosphoinositide-polyglycerophospholipid pathway; and 2) these phospholipids are involved in the steroidogenic action of ACTH.