Abstract

Effects of vasodilating drugs were compared in helical strips of canine basilar, coronary and mesenteric arteries contracted with K⁺. Papaverine caused a dose-dependent relaxation, the maximum relaxation being attained at 10^-4 M in these three arteries. Adenosine and NaNO₂, also produced relaxation, and the difference in dose-response relationships in these arteries was only slight. Similar relaxation in response to adenosine was observed in human basilar arteries. Relaxation induced by isoproterenol was appreciably greater in coronary arterial strips than in mesentenic arteries. Relaxation in basilar arteries of dogs and humans was slight even at high concentrations. Acetylcholine elicited a dose-realted relaxation in coronary arteries which was inhibited by treatment with atropine but not by propranolol. In basilar arteries, only a slight relaxation was produced. In mesenteric arterial strips, acetylcholine produced biphasic responses, relaxation at low concentrations and contraction at high concentrations. The contraction was reversed to a relaxation by phenoxybenzamine. The release of catecholamines may be involved in the genesis of the acetylcholine-induced contraction. It appears that as far as basilar arteries are concerned, adrenergic and cholinergic vasodilator mechanisms do not play a major role in the regulation of the vascular tone.