Vascular dysfunction in streptozotocin-induced experimental diabetes strictly depends on insulin deficiency

In previous studies we and others have shown that streptozotocin (STZ)-induced diabetes in rats is associated with vascular oxidative stress and dysfunction. In the present study, we sought to determine whether vascular dysfunction and oxidative stress strictly depend on insulin deficiency.

The effects of insulin (2.5 U/day s.c., 2 weeks) therapy on vascular disorders in STZ-induced (60 mg/kg i.v., 8 weeks) diabetes mellitus (type I) were studied in Wistar rats. The contribution of NADPH oxidase to overall oxidative stress was investigated by in vivo (30 mg/kg/day s.c., 4 days) and in vitro treatment with apocynin.

Insulin therapy completely normalized blood glucose, body weight, vascular dysfunction and oxidative stress as well as increased cardiac reactive oxygen and nitrogen species formation in diabetic rats, although diabetes was already established for 6 weeks before insulin therapy was started for the last 2 weeks of the total treatment interval. Apocynin normalized cardiac NADPH oxidase activity, and L-NAME effects suggest a role for uncoupled endothelial nitric oxide synthase in diabetic vascular complications.

Our findings indicate that STZ-induced diabetes is a model of insulin-dependent diabetes (type 1) and that cardiovascular complications are probably not associated with systemic toxic side effects of STZ.