Recent studies have shown that NO acts as a negative inotrope and chronotrop in cardiac muscle. In the present study, we investigated the effects of the chronic administration of L-NAME and L-arginine on 14-week streptozotocin (STZ)-diabetic rat atria. To study these effects, we compared the alterations of inotropic and chronotropic responses to isoprenaline (ISO) on electrically-driven left atria and spontaneously beating right atria. In addition, we compared the blood pressures of rats in all groups. The chronic administration of L-arginine resulted in a significant reduction in blood pressure of the diabetic rats. On the other hand, the chronic nitric oxide synthase inhibition resulted in a significant increase in blood pressure of diabetic animals. To our findings, maximum positive inotropic responses of ISO diminished in STZ-diabetic, L-arginine and L-NAME treated diabetic groups relative to controls but neither the basal contractility of the left atria nor the pD(2) values were altered significantly in all groups. The basal atrial rate and maximum positive chronotropic responses to ISO were found to be significantly lower in treated and untreated diabetic groups, no significant changes were observed in pD(2) values. Our results demonstrate that the changes in inotropic and chronotropic responses in diabetic rat atria were not influenced by the chronic administration of L-arginine and L-NAME treatments. (C) 2000 Academic Press.