Human pancreatic GRF stimulates phosphatidylinositol labeling in cultured anterior pituitary cells

The effects of natural and synthetic human pancretic growth hormone-releasing factor (hpGRF) on ³²P incorporation into phospholipids were studied in cultured rat anterior pituitary cells. Natural hpGRF (1:30 dilution) significantly (P < 0.01) stimulated phosphatidylinositol labeling at all times studied (15, 30, and 60 min). Synthetic hpGRF-(1-40)OH also significantly (P < 0.05; P < 0.01) increased ³²P incorporation into phosphatidylinositol in a dose-related (1-30 nM) and time-dependent (5, 10, and 30 min) manner. In contrast, phosphatidylcholine and phosphatidylethanolamine labeling was not affected at any time studied. Somatostatin (30 nM) did not affect basal or hpGRF-stimulated phosphatidylinositol labeling but inhibited the hpGRF stimulation of cyclic AMP accumulation and growth hormone release. These results suggest that the phosphatidylinositol cycle may be involved in the mechanism of action of hpGRF in the anterior pituitary gland.