Constrictor responses of the rat basilar artery during diabetes mellitus

Diabetes mellitus produces abnormalities of the endothelium and impairs endothelium-dependent dilatation of large and small cerebral blood vessels. However, the effect of diabetes mellitus on cerebral vasoconstriction and the modulatory influence of nitric oxide on cerebral vasoconstriction is unclear. Thus, the first goal of this study was to examine the effect of diabetes mellitus on constrictor responses of the basilar artery in vivo. Our second goal was to examine a potential role for nitric oxide in modulating constrictor responses of the basilar artery. A craniotomy was performed over the ventral medulla to expose the basilar artery. The diameter of the basilar artery was measured using intravital microscopy in nondiabetic and diabetic (3-4 months after injection of streptozotocin; 50-60 mg/kg i.p.) rats in response to angiotensin II, arginine vasopressin, endothelin-1, and the thromboxane analogue, U-46619. Topical application of angiotensin II (10 and 100 nM) produced only minimal changes in diameter of the basilar artery which were similar in nondiabetic and diabetic rats (p>0.05). Arginine vasopressin (0.1 and 1.0 nM), endothelin-1 (10 and 50 nM), and U-46619 (10 and 100 nM) produced marked dose-related constriction of the basilar artery which also was similar in nondiabetic and diabetic rats (p>0.05). Next, we examine whether the synthesis/release of nitric oxide played a role in constriction of the basilar artery in response to the agonists. We found that L-NMMA (1.0 microM) did not alter constrictor responses of the basilar artery in nondiabetic and diabetic rats. Thus, responses of the basilar artery to important vasoactive agonists are not altered by diabetes mellitus. In addition, it does not appear that the synthesis/release of nitric oxide modulates constrictor responses of the basilar artery to angiotensin II, arginine vasopressin, endothelin-1 and U-46619. We suggest that preservation of vasoconstrictor responses, coupled with impaired vasodilator responses, may contribute to the pathogenesis of cerebrovascular abnormalities associated with diabetes mellitus.