Potassium relaxation of vascular smooth muscle from DOCA hypertensive pigs

This study was designed to characterize potassium-induced relaxation in vascular smooth muscle during the development of deoxycorticosterone acetate (DOCA) hypertension. Pigs were implanted subcutaneously with 100 mg/kg DOCA. Mean arterial pressure in the DOCA-treated pigs reached levels approximately 37% greater than controls. In some pigs, the left hindlimb vascular bed was "protected" from the rise in arterial pressure by ligation of the iliac artery. Arterial strips from DOCA hypertensive and normotensive pigs relaxed in response to potassium after contraction induced by norepinephrine in potassium-free solution. Arterial strips from DOCA hypertensive pigs showed greater relaxation than did those from normotensive pigs. The magnitude of relaxation in femoral arteries from "protected" hindlimbs was similar to that in arteries from the contralateral unoccluded limb. Potassium-induced relaxation in tail arteries from DOCA hypertensive pigs was more sensitive to ouabain inhibition than that from normotensive pigs. Relaxation induced by potassium varied with: 1) length of incubation in potassium-free solution; 2) concentration of added potassium; and 3) concentration of norepinephrine added during the potassium-free interval. The amplitude of potassium-induced relaxation is believed to be a functional index of the activity of the electrogenic sodium-potassium transport system. These experiments support the hypothesis that vascular smooth muscle from DOCA hypertensive animals has increased electrogenic sodium pump activity. The development of this vascular change parallels the increase in blood pressure induced by mineralocorticoid excess.