Central insulin regulates heart rate and arterial blood flow: an endothelial nitric oxide synthase-dependent mechanism altered during diabetes.

Objective: Central neural insulin regulates glucose homeostasis, but less is known about its cardiovascular effects. Endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) represents a molecular link between metabolic and cardiovascular disease. Its role in the central nervous system remains to be determined. We studied the effects of central insulin infusion on femoral arterial blood flow and heart rate in normal chow-fed, high-fat diet-fed diabetic, and eNOS-null mice.
Research Design and Methods: We recorded heart rate and femoral blood flow (ultrasonic flow probe) during 3-h central insulin infusion in conscious, freely moving mice. To study the role of NO in this setting, we assessed total and phosphorylated eNOS in the hypothalamus and examined the effects of brain infusion of NO donors/NOS inhibitors on cardiovascular responsiveness to central insulin in these experimental mouse models.
Results: In normal mice, central insulin rapidly increased heart rate by 30% and more progressively increased blood flow by 40%. In high-fat diet-fed mice, the cardiovascular effects of insulin were blunted and associated with a 50% reduction of the total and phosphorylated eNOS expression in the hypothalamus, suggesting a causal link. In line with this hypothesis, in eNOS-null mice and central N(G)-monomethyl-L-arginine-infused normal mice, the cardiovascular effects of insulin were abolished, whereas central NO donor infusion restored these effects in eNOS-null mice. In high-fat diet-fed mice, central NO donor infusion mimicked the cardiovascular responses evoked by central insulin in normal mice.
Conclusions: Central insulin has cardiovascular effects in conscious, freely moving mice that are mediated, at least in part, by central neural eNOS. These effects are impaired in insulin-resistant high-fat diet-fed mice.