Evidence for increased functional vascular Na+/K+ pump activity in the obese Zucker rat

Insulin is known to stimulate Na+/K+ ATPase and to relax vascular smooth mu scle. We hypothesized that vascular tone in the obese Zucker (fa/fa) rat, a hyperinsulinemic model in which hypertension can develop, may be influence d by insulin's ability to stimulate Na+/K+ ATPase at the vascular level. We studied isometric preparations of tail and femoral arteries from 10-wk-old , male obese Zucker rats, which were hyperinsulinemic but still normotensiv e us. lean controls. Sensitivity to potassium-induced relaxations, an index of vascular Na+/K+ ATPase activity was significantly greater in the obese Zucker rat than control. Sensitivity to transmural-nerve-stimulation-induce d contractions was decreased in the femoral and tail arteries from obese ra ts as compared with lean controls. Insulin (50 to 200 mU/ml) mimicked potas sium-induced relaxations in the femoral artery, an effect that was signific antly greater in the obese group. These data suggest that in the young hype rinsulinemic Zucker rat, insulin has a stimulatory effect on the vascular N a+/K+ pump, which may be associated with a decreased presynaptic adrenergic influence on vascular tone. Development of resistance to these vascular re laxant effects of insulin with advancing age might contribute to the onset of hypertension in this model.