Insulin reverses hypertension and hypothalamic depression in streptozotocin diabetic rats

Daily subcutaneous injections of lente insulin reduced the hypertension and bradycardia which developed consistently in streptozotocin diabetic rats. Insulin-treated rats also became less hyperglycemic, drank less water, and gained weight faster than untreated diabetic controls. Behavioral and tachycardiac effects elicited by electrical stimulation of the ventromedial hypothalamus while the rats were awake were similar, but attendant pressor responses were larger in those that had been treated with insulin. Under subsequent urethane anesthesia, pressor and sympathetic responses to hypothalamic stimulation, as well as pressor responses to tyramine and vasopressin, were augmented in insulin-treated rats. A generalized increase in cardiovascular reactivity caused by insulin seemed unlikely since pressor responses to norepinephrine were unaltered. Enhanced hypothalamic responsiveness was considered due to improvement of diabetic encephalopathy rather than to direct CNS stimulation by insulin because the injected insulin had mostly dissipated by the time pressor responses were recorded. By showing that insulin treatment produced changes opposite to those occurring during induction of diabetes our results suggest that insulin can alleviate cardiovascular and hypothalamic dysfunction in streptozotocin-induced diabetes.