INVITRO DIFFERENCES BETWEEN HUMAN ARTERIES AND VEINS IN THEIR RESPONSES TO HYDRALAZINE

Abstract

The inhibitory action of hydralazine on the contractility of human blood vessels was examined by using in vitro human digital artery and metacarpal vein preparations obtained postmortem. Cumulative contractile concentration-effect curves were performed to norepinephrine, 5-hydroxytryptamine, histamine, angiotensin, KCl and BaCl2 in both arteries and veins. With the exception of BaCl2, hydralazine shifted the concentration-effect curves to the right and reduced the maximum responses to these agonists. This effect was markedly greater in arteries than in veins in which hydralazine had no effect. The maximum responses to the agonists norepinephrine, 5-hydroxytryptamine and KCl were markedly reduced when the normal bathing solution was replaced by a Ca-free solution, and for each agonist this effect was much greater in veins than arteries. The responses to BaCl2 were not significantly altered by the Ca-free bathing solution. Human arteries are evidently much more sensitive to the effects of hydralazine than are human veins and the mechanism of action of hydralazine is probably due to inhibition of the release of tightly bound Ca ions.