1. The characteristics of vasopressin-stimulated phosphatidylinositol 4,5 bisphosphate (PtdIns(4,5)P2) and phosphatidylcholine (PtdCh) hydrolysis were examined in A10 vascular smooth muscle cells (VSMC), by assessing the formation of [3H]-inositol phosphates ([3H]-IP) and the accumulation of the phospholipase D (PLD) specific product, [3H]-phosphatidylbutanol ([3H]-PtdBuOH). 2. Vasopressin ([Arg8]-VP) and a number of related analogues stimulated the accumulation of [3H]-IP and [3H]-PtdBuOH with similar EC50 values, generating the same rank order of potency for each response (Arg8-VP = vasotocin = Lys8-VP much greater than oxytocin). 3. Inhibition of vasopressin-stimulated [3H]-IP and [3H]-PtdBuOH accumulation by the V1a receptor antagonists, Des-Gly9[beta-mercapto-beta,beta,-cyclopentamethylene propionyl, O-Et-Tyr2,Val4,Arg8]-vasopressin generated similar IC50 values suggesting that both these responses are mediated through the activation of a single V1a receptor subtype. 4. The onset of vasopressin-stimulated inositol-1,4,5-trisphosphate (Ins(1,4,5)P3) mass formation preceded [3H]-PtdBuOH accumulation indicating that PtdCh hydrolysis was activated subsequent to PtdIns(4,5)P2 breakdown. 5. The protein kinase C (PKC) activator, tetradecanoylphorbol acetate (TPA) also stimulated [3H]-PtdBuOH accumulation. Preincubation with the PKC inhibitor Ro-31-8220 abolished both TPA- and vasopressin-stimulated [3H]-PtdBuOH, suggesting that the intermediate activation of protein kinase C is involved in the regulation of PLD by vasopressin. 6. Pretreatment of the A10 VSMC with Ro-31-8220 (100 microM) also potentiated vasopressin-stimulated Ins(1,4,5)P3 mass formation.(ABSTRACT TRUNCATED AT 250 WORDS)