The present study was to investigate the mechanism by which AVP increases insulin secretion in RINm5F cells. A specific PLC inhibitor, U-73122, and a PLA2 inhibitor, N-(p-amylcinnamoyl)anthranilic acid (ACA) were used. U-73122 (2-8 [mu]M) inhibited the AVP-induced increases in the intracellular concentration of inositol 1,3,4-trisphosphate and (Ca2+]i dose-dependently. U-73122 (8 [mu]M) abolished the AVP's effect on IP3 and (Ca2+]i, but it only reduced the AVP-induced increase in insulin secretion by 35%. The discrepancy between the results of (Ca2+]i and insulin secretion may be due to the multiple signal transduction pathways. ACA (100 [mu]M) didn't antagonize the AVP-induced increase in insulin release. These results suggested: (1) U-73122 blocks PLC activities but fails to block other signal transduction pathways that trigger insulin secretion in these cells, and (2) AVP increases insulin release from RINm5F cells through both the PLC mediated Ca2+-dependent and Ca2+-independent pathways;We investigated the effect of the antifungal antibiotic wortmannin, a PLD inhibitor, on AVP-induced increases in insulin secretion and (Ca2+]i. Wortmannin (0.1-1 [mu]M) inhibited AVP-induced increase of insulin secretion dose-dependently. The combination of wortmannin and U-73122, had an additive inhibition on the AVP-induced insulin secretion. However, wortmannin failed to change the AVP-induced increase of (Ca2+]i. These results suggested: (1) activation of PLD stimulated at least partially the AVP-induced insulin secretion, (2) PLD didn't influence the AVP-elicited elevation of (Ca2+]i and, (3) PLC and PLD stimulate AVP-activated signal transduction in an independent manner;Ro 31-8220, a specific PKC inhibitor, dose-dependently potentiated the AVP-induced increase of insulin secretion and elevation of (Ca2+]i. The potentiation of AVP-induced elevation of (Ca2+]i by Ro 31-8220 was mediated by an increase in Ca2+ influx. Treatment with a DAG analog, OAG, inhibited AVP-induced insulin dose-dependently, but reduced slightly effect the AVP-induced elevation of (Ca2+]i. Activation of PKC by OAG had no effect on insulin secretion and (Ca2+]i. These results suggested: (1) PKC is a negative regulator of AVP's action in beta-cells, (2) PKC inhibits the Ca2+ channels to regulate insulin secretion.