Changes in Vascular Contractility in Rats with Sub-chronic Diabetes Induced by Streptozotocin

To study the induction and promotion of atherosclerosis in diabetes, vascular responsiveness in streptozotocin (STZ) -treated diabetic rats was examined. After intravenous injection of STZ (50 mg/kg, 2 times) to female Wistar rats (6 weeks), levels of plasma glucose were higher than in age-matched control animals. At 6 and 10 weeks after the onset of diabetes, the ratio of liver and kidney weight to body weight was increased, and plasma amylase activity was decreased. At 6 weeks, urea nitrogen content and transaminase activity in plasma were significantly increased. Vascular contractility in response to 5-30 mM potassium chloride (KCl), 5 × 10-8-10-5M 5-hydroxytryptamine (5-HT), 5 × 10-5-5 × 10-3 M histamine, and 5 × 10-910-6 M norepinephrine (NE) was examined in isolated rat aorta. At 6 weeks after the onset of diabetes, sensitivity of the aorta to KCl and 5-HT were significantly depressed compared to nondiabetic controls. Responses of the aorta to histamine and NE were increased in diabetic rats at 10 weeks. The results suggest that sustained high plasma glucose induces a change in the sensitivity of smooth muscle cells in the aorta, and these changes may contribute to the induction and promotion of atherosclerosis in sub-chronic diabetes induced by STZ.