On the source of the vasopressin-induced increases in diacylglycerol in hepatocytes

In hepatocytes pre-labelled with [³H]glycerol, vasopressin increased by 20% the amount of radioactivity present in diacylglycerols. The effect of vasopressin was partially dependent on Ca²⁺. The magnitude of the increase in [³H]diacylglycerol was 5-times the sum of the radioactivity present in phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate. No stimulation by vasopressin of the initial rate of incorporation of radioactivity into diacylglycerols was observed in cells incubated in the presence of 10 mM [³H]glycerol. Treatment of hepatocytes labelled with either [³H]ethanolamine or [³H]choline with vasopressin, ionophore A23187 or phospholipase C increased the amount of radioactivity present in trichloroacetic acid extracts of the cells. The effect of vasopressin was dependent on extracellular Ca²⁺. It is concluded that in hepatocytes vasopressin increases diacylglycerols by a process which does not principally involve the conversion of phosphoinositides to diacylglycerol or the de novo synthesis of diacylglycerol from glycerol 3-phosphate, but does involve the Ca²⁺-dependent conversion of phosphatidylethanolamine and phosphatidylcholine to diacylglycerol.