Antihypertensive effect of insulin via nitric oxide production in the Zucker diabetic fatty rat, an animal model for non-insulin-dependent diabetes mellitus

It has been reported that insulin treatment improves hypertension in patients with diabetes mellitus. The mechanisms of the antihypertensive effect of insulin, however, remain to be fully elucidated. In the present study, we investigated a possible involvement of nitric oxide (NO) in insulin-induced reduction of blood pressure using the Zucker diabetic fatty (ZDF) rat, an animal model of non-insulin-dependent diabetes mellitus. The animals were divided into three groups and treated for 4 weeks with daily subcutaneous injections of insulin (25U/kg body weight) with or without oral administration of l-nitro-arginine methyl ester (L-NAME, 50mg/kg/day body weight as drinking water), an inhibitor of NO synthase (NOS). Saline solution was injected subcutaneously in the control groups. During the experimental period, body weight gain was greater in the insulin-treated groups than in the control groups whereas water intake was considerably decreased in the insulin-treated groups. Insulin treatment resulted in a decrease in plasma glucose and blood pressure, and an increase in both NO metabolites (NOx) in the plasma and NOS activity in the aorta tissue. L-NAME treatment blunted not only the antihypertensive effect of insulin but also the changes in NOx and NOS activity. These findings suggest that insulin reduces blood pressure in the ZDF rat by stimulating NOS activation and NO production.