A chronic physical activity treatment in obese rats normalizes the contributions of ET-1 and NO to insulin-mediated posterior cerebral artery vasodilation

Abstract

This study tested the hypotheses that obesity-induced decrements in insulin-stimulated cerebrovascular vasodilation would be normalized with acute endothelin-1a receptor antagonism and that treatment with a physical activity intervention restores vasoreactivity to insulin through augmented nitric oxide synthase (NOS)-dependent dilation. Otsuka Long-Evans Tokushima Fatty rats were divided into the following groups: 20 wk old food controlled (CON-20); 20 wk old free food access (model of obesity, OB-20); 40 wk old food controlled (CON-40); 40 wk old free food access (OB-40); and 40 wk old free food access+RUN (RUN-40; wheel-running access from 20 to 40 wk). Rats underwent Barnes maze testing and a euglycemic hyperinsulinemic clamp (EHC). In the 40-wk cohort, cerebellum and hippocampus blood flow (BF) were examined (microsphere infusion). Vasomotor responses (pressurized myography) to insulin were assessed in untreated, endothelin-1a receptor antagonism, and NOS inhibition conditions in posterior cerebral arteries. Insulin-stimulated vasodilation was attenuated in the OB vs. CON and RUN groups (<i>P</i> ≤ 0.04). Dilation to insulin was normalized with endothelin-1a receptor antagonism in the OB groups (between groups, <i>P</i> ≥ 0.56), and insulin-stimulated NOS-mediated dilation was greater in the RUN-40 vs. OB-40 group (<i>P</i> < 0.01). At 40 wk of age, cerebellum BF decreased during EHC in the OB-40 group (<i>P</i> = 0.02) but not CON or RUN groups (<i>P</i> ≥ 0.36). Barnes maze testing revealed increased entry errors and latencies in the RUN-40 vs. CON and OB groups (<i>P</i> < 0.01). These findings indicate that obesity-induced impairments in vasoreactivity to insulin involve increased endothelin-1 and decreased nitric oxide signaling. Chronic spontaneous physical activity, initiated after disease onset, reversed impaired vasodilation to insulin and decreased Barnes maze performance, possibly because of increased exploratory behavior.<b>NEW & NOTEWORTHY</b> The new and noteworthy findings are that <i>1</i>) in rodents, obesity-related deficits in insulin-mediated vasodilation are associated with increased influence of insulin-stimulated ET-1 and depressed influence of insulin-stimulated NOS and <i>2</i>) a physical activity intervention, initiated after the onset of disease, restores insulin-mediated vasodilation, likely by normalizing insulin-stimulated ET-1 and NOS balance. These data demonstrate that the treatment effects of chronic exercise on insulin-mediated vasodilation extend beyond active skeletal muscle vasculature and include the cerebrovasculature.