Synergism between vasopressin and phorbol esters in stimulation of insulin secretion and phosphatidylcholine metabolism in RIN insulinoma cells.

The tumor promoter, tetradecanoylphorbolacetate (TPA), causes a significant increase in both insulin secretion and the incorporation of 32Pi into phosphatidylcholine (PC) in RIN insulinoma cells. The peptide hormone, arginine vasopressin (AVP), also stimulates these functions, although to a lesser degree. When added together, the effects on secretion and PC metabolism are synergistic. At the same time, TPA inhibits the AVP-stimulated rise in phosphoinositide (PI) metabolism. Neither phloretin nor tamoxifen, reported to be inhibitors of protein kinase C activity, are able to block the effects of TPA on secretion, although both influence PC metabolism.