The effects of insulin on vasoconstrictor responses in pithed rats

Pressor responses to spinal sympathetic outflow and selected vasoactive agents were examined in control and diabetic Wistar-Kyoto pithed rats. Diabetes was induced by intravenous injection of alloxan (50 mg/kg). One week after the diabetogen, some of the rats were treated with one daily subcutaneous injection of Lente insulin (2 U/100 Gm) for five weeks. All rats were pithed at six weeks after alloxan. Vasoconstrictor responses to spinal sympathetic outflow, serotonin, norepinephrine, tyramine, and angiotensin were reduced in diabetic rats as compared to their age-matched controls. Administration of insulin caused only partial normalization of these responses. Nondiabetic rats given insulin exhibited vascular responsiveness similar to the treated diabetic group of animals. Blood pressures and heart rates were also found to be similar between the insulin-treated groups and significantly less than control. The finding that insulin does not produce complete normalization of vasoconstrictor responsiveness in diabetic rats may be relevant to the reduced blood pressure observed following insulin treatment.