Abstract

Rat adrenocortical cells and preparations of plasma membrane and mitochondria have been employed to assess the effects of phospholipids and of sterol carrier protein 2 (SCP 2) on specific aspects of adrenal steroidogenesis. With intact cells, liposomal dispersions of cardiolipin caused significant stimulation of corticosterone output, while preparations of phosphatidylcholine, phosphatidylinositol, or the 4'-phosphate and the 4',5'-diphosphate derivatives of phosphatidylinositol were without effect. With the adrenal plasma membrane preparation, none of the added phospholipids affected either sodium fluoride or ACTH-responsive adenylate cyclase activity. With intact mitochondria, only cardiolipin, among the various phospholipids, tested, caused a concentration-dependent stimulation of pregnenolone production. However, even at the highest concentration of cardiolipin tested (500 μM), the stimulatory effect was only half that observed with 0.7 μM SCP 2, and the two effectors were not synergistic. SCP 2 caused a redistribution of cholesterol from mitochondrial outer to inner membranes, while cardiolipin, which is an activator of cytochrome P-450 scc , had no effect on distribution of mitochondrial membrane cholesterol.

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