VASOCONSTRICTOR RESPONSES OF ISOLATED AND PERFUSED CANINE MESENTERIC-ARTERIES TO ALPHA-ADRENOCEPTOR AGONISTS

Abstract

Using isolated and perfused canine mesenteric artery, vasoconstrictor responses to .alpha.-adrenoceptor stimulating agents were compared. Potency order for inducing vasoconstriction was epinephrine > norepinephrine > phenylephrine > methoxamine > dopamine .mchgt. tyramine > clonidine .gtoreq. xylazine. A selective .alpha.2-stimulant, xylazine, did not induce any significant vasoconstrictor response. Tyramine produced only a slight vasoconstriction. Responses to norepinephrine, phenylephrine and methoxamine were competitively inhibited by phentolamine treatment. The adrenoceptor in the canine mesenteric artery may be characterized as an .alpha.1-receptor and norepinephrine release by tyramine is not marked in this relatively large vessel.