Luteinizing Hormone-Releasing Hormone Stimulates Arachidonic Acid Release in Rat Granulosa Cells*

The effect of LHRH on arachidonic acid release was studied in rat granulosa cells in primary culture. In cells prelabeled with [3H]arachidonic acid, LHRH caused an increase in the level of [3H]arachidonic acid released in the culture medium, to 125-150% of control levels at the end of a 60-min incubation period. In subsequent time-course and dose-response experiments, a significant effect on [3H]arachidonic acid release could be observed as early as 15 min after LHRH addition, and the lowest effective dose was 10(-8) M LHRH. Addition of LH, FSH, prostaglandin F2 alpha, or (Bu)2cAMP was without effect. Likewise, an agonistic LHRH analog (LHRHa, 10(-8) M) also markedly stimulated [3H]arachidonic acid from cultured granulosa cells, and the effects of both LHRH and LHRHa were blocked by concomitant presence of a potent LHRH antagonist. In addition to [3H]arachidonic acid release in the culture medium, the effect of LHRH on the level of radiolabel present in cellular phospholipids was also examined. In granulosa cells prelabeled with [3H] arachidonic acid, LHRH significantly depleted the level of radioactivity previously incorporated into cellular phosphatidylinositol, as early as 5 min after its addition, to 85% of control levels. The level of radiolabel found in other major phospholipids such as phosphatidylserine/phosphatidylcholine and phosphatidylethanolamine, as well as the intracellular level of unesterified [3H]arachidonic acid, were not significantly affected by LHRH. The effect of LHRH on [3H]arachidonic acid release from prelabeled phospholipids as well as the LHRH-induced loss of radioactivity previously incorporated into phosphatidylinositol could be reversed by verapamil, suggesting a possible calcium dependency. Taken together, these data support the notion that arachidonic acid liberation from phospholipids may be associated with the mechanism of action of LHRH on ovarian cells.