The role of the phosphatidate-inositide cycle in the action of steroidogenic agents.

Most steroidogenic agents have been found to provoke rapid changes in the metabolism of phospholipids in the phosphatidate-inositide cycle. These changes include: (a) de novo synthesis of phosphatidic acid and its derivatives, phosphatidylglycerol, mono- and polyphosphoinositides and diglyceride; and (b) phosphatidylinositol hydrolysis and consequent generation of diglyceride and phosphatidic acid. The de novo phosphatidate synthesis effect occurs in the action of all tested steroidogenic agents (ACTH, LH, angiotensin, K+, serotonin) and may be induced by either of the "second messengers", cAMP and Ca2+. The phosphatidylinositol hydrolysis effect(s) occurs only in the action of steroidogenic agents that operate via Ca2+ (angiotensin and K+) and may be important in Ca2+ mobilization. The de novo phospholipid effect correlates well with changes in steroidogenesis and, like the latter, requires Ca2+ and protein synthesis; from these and other results, it seems likely that this phospholipid effect plays an important role in the stimulation of steroidogenesis.