It has been reported that nitric oxide (NO) is a positive modulator of glucagon release. The involvement of cyclic guanosine 3,5-monophosphate (cGMP) in NO-induced glucagon secretion and the possible role of NO in glucagon release induced by L-arginine were investigated in mouse clonal โฃ-cell line clone 6 (โฃTC6) cells, which predominantly secrete glucagon. NOC12, an NO donor, elicited an increase in glucagon release from โฃTc6 cells in perifusion and static incubation. An inhibitor of cGMP-dependent protein kinase inhibited NOC12-induced glucagon release. NOC12 (1 mmol/L) also increased the cellular level of cGMP. In addition, a permeable cGMP agonist increased glucagon release. L-arginine (15 mmol/L) increased perifusate concentrations of glucagon and nitrite in โฃTc6 cells, which were inhibited by N G -nitro-L-arginine methyl ester. NO synthase (NOS) activity was shown in โฃTc6 cells by L-citrulline formation assay. Our present findings suggest that NO plays a stimulating role in glucagon release from the โฃ cells, and that a cGMP-dependent pathway is involved in NO action. These findings also provide further evidence that L-arginine might play a stimulating role in regulating glucagon secretion, at least partly, through generation of NO in the islets.