The vascular Na+-K+ pump in experimental hypertension.

We assessed the role of putative circulating ouabainlike factor(s) on in vivo arteriolar function in rats with very early (less than 7 days; mean, 3 days) and chronic (greater than 4 weeks) benign, one-kidney, one clip (1K1C) hypertension. Thus, we measured vascular responses in vasodilated (nitroprusside or adenosine), vascularly isolated, innervated hindlimb vascular beds of chloralose-anesthetized 1K1C rats perfused with their own blood at 1 ml/min. Complete norepinephrine dose-response curves in 8 rats with chronic and 28 with early 1K1C hypertension, compared with appropriate normotensive control rats, showed unchanged thresholds and ED50 values. Magnitude of ouabain-induced leftward shifts of the norepinephrine dose-response curve in 18 rats with chronic and 21 with early 1K1C hypertension, compared with appropriate normotensive control rats, was unchanged. Blockade of neural uptake of norepinephrine by desimipramine (10(-7) M) in 8 1K1C rats did not alter these results. These findings provide no evidence in this form and these stages of hypertension that humoral ouabainlike inhibitors of the Na+-K+ pump evoke physiologically significant inotropic effects in arterioles in vivo. It is possible, however, that induction of vascular Na+-K+-adenosine triphosphatase by circulating inhibitors modified the vascular responses to norepinephrine and ouabain in these rats.