LHRH rapidly stimulates phosphatidylinositol metabolism in enriched gonadotrophs

The effects of luteinizing hormone-releasing hormone (LHRH) and human pancreatic growth hormonereleasing factor (hpGRF(l-40)-NH₂) on phospholipid metabolism were studied in rat anterior pituitary cells in primary culture. In a 4-fold enriched population of gonadotrophs, 30 nM LHRH increased ³²P; incorporation into phosphatidic acid (PA) as early as l min after its addition. Phosphatidylinositol (PI) labeling was increased l min later. The stimulatory action of LHRH was observed in both phospholipids up to 100 min, the last time interval studied. The decapeptide did not affect ³²P_i labeling of phosphatidylcholine (PC), lysoPC, phosphatidylethanolamine or phosphatidylserine. Dose-response studies performed after 25 min of incubation showed an ED₅₀ value of LHRH action at approximately 1 nM for PI labeling. In contrast, the addition of 0.1 μM GRF to anterior pituitary cells enhanced ³²P_i incorporation only into PC after a 60 min incubation period. The present data suggest that stimulation of acidic phospholipid metabolism, particularly an increase in PA-PI turnover, may represent an early event in the mechanism of action of LHRH but not GRF in the anterior pituitary gland.