The effects of chronic L-name and L-arginine administration on beta-adrenergic responsiveness of STZ-diabetic rat atria

Recent studies have shown that NO acts as a negative inotrope and chronotro p in cardiac muscle. In the present study, we investigated the effects of t he chronic administration of L-NAME and L-arginine on 14-week streptozotoci n (STZ)-diabetic rat atria. To study these effects, we compared the alterat ions of inotropic and chronotropic responses to isoprenaline (ISO) on elect rically-driven left atria and spontaneously beating right atria. In additio n, we compared the blood pressures of rats in all groups. The chronic admin istration of L-arginine resulted in a significant reduction in blood pressu re of the diabetic rats. On the other hand, the chronic nitric oxide syntha se inhibition resulted in a significant increase in blood pressure of diabe tic animals. To our findings, maximum positive inotropic responses of ISO d iminished in STZ-diabetic, L-arginine and L-NAME treated diabetic groups re lative to controls but neither the basal contractility of the left atria no r the pD(2) values were altered significantly in all groups. The basal atri al rate and maximum positive chronotropic responses to ISO were found to be significantly lower in treated and untreated diabetic groups, no significa nt 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 treat ments. (C) 2000 Academic Press.