nNOS-dependent reactivity of cerebral arterioles in Type 1 diabetes

Abstract

Our goals were to determine whether Type 1 diabetes (T1D) alters neuronal nitric oxide synthase (nNOS)-dependent reactivity of cerebral arterioles and to identify a potential role for oxidative stress in T1D-induced impairment in nNOS-dependent responses of cerebral arterioles. Rats were injected with vehicle (sodium citrate buffer) or streptozotocin (50 mg/kg IP) to induce T1D. Two to three months later, we measured functional responses of cerebral arterioles to nNOS-dependent (NMDA and kainate) and -independent (nitroglycerin) agonists in nondiabetic and diabetic rats before and during inhibition of oxidative stress using tempol (100 microM). In addition, we measured superoxide anion production under basal conditions, during stimulation with NMDA and kainate, and during treatment with tempol. We found that nNOS-dependent, but -independent, vasodilatation was impaired in diabetic compared to nondiabetic rats. In addition, treatment of the cerebral microcirculation with tempol restored impaired nNOS-dependent vasodilatation in diabetic rats toward that observed in nondiabetic rats. Furthermore, the production of superoxide anion (lucigenin chemiluminescence) was increased in parietal cortical tissue of diabetic rats under basal conditions. Application of NMDA and kainate did not increase superoxide anion production in nondiabetic or diabetic rats. However, tempol decreased basal production of superoxide anion in diabetic rats. Our findings suggest that T1D impairs nNOS-dependent dilatation of cerebral arterioles by a mechanism that appears to be related to the formation of superoxide anion.

Figure 1

Response of cerebral arterioles to NMDA in nondiabetic rats before (n=6; open bars) and during (right hatched bars) treatment with tempol (100 μM), and in diabetic rats before (n=6; closed bars) and during (cross hatched bars) treatment with tempol. Values are means±SE. *p< 0.05 versus response in nondiabetic rats before and during treatment with tempol, and in diabetic rats during treatment with tempol.

Figure 2

Response of cerebral arterioles to kainate in nondiabetic rats before (n=6; open bars) and during (right hatched bars) treatment with tempol (100 μM), and in diabetic rats before (n=6; closed bars) and during (cross hatched bars) treatment with tempol. Values are means±SE. *p< 0.05 versus response in nondiabetic rats before and during treatment with tempol, and in diabetic rats during treatment with tempol.

Figure 3

Response of cerebral arterioles to nitroglycerin in nondiabetic rats before (n=6; open bars) and during (right hatched bars) treatment with tempol (100 μM), and in diabetic rats before (n=6; closed bars) and during (cross hatched bars) treatment with tempol. Values are means±SE.

Figure 4

Superoxide anion production from parietal cortical tissue in nondiabetic (n=10; open bars) and diabetic (n=18; closed bars) rats under basal conditions, during treatment with tempol (100 μM), during treatment with NMDA (300 μM) and during treatment with kainate (300 μM). Values are means ± SE. * p < 0.05 versus nondiabetic rats under basal conditions and ** p < 0.05 during treatment with tempol.