text: 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.
  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.