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 muscle. We hypothesized that vascular tone in the obese Zucker (fa/fa) rat, a hyperinsulinemic model in which hypertension can develop, may be influenced 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 normotensive vs. 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-induced contractions was decreased in the femoral and tail arteries from obese rats as compared with lean controls. Insulin (50 to 200 mU/ml) mimicked potassium-induced relaxations in the femoral artery, an effect that was significantly greater in the obese group. These data suggest that in the young hyperinsulinemic Zucker rat, insulin has a stimulatory effect on the vascular Na+/K+ pump, which may be associated with a decreased presynaptic adrenergic influence on vascular tone. Development of resistance to these vascular relaxant effects of insulin with advancing age might contribute to the onset of hypertension in this model.