title: Effects of naloxone on canine cerebral vascular smooth muscle.
abstract: The pharmacological effects of naloxone on cerebral arterial smooth muscle in vitro were examined using canine basilar arterial strips. Naloxone exerted two different effects on canine basilar artery: (1) at a high concentration (3 X 10(-4) M) it produced nonspecific vasodilation, and (2) at lower concentrations (3 X 10(-7), 3 X 10(-6), and 3 X 10(-5) M) it inhibited the vasoconstrictor effects of norepinephrine without altering KCl-, serotonin-, or hemoglobin-induced constriction. Morphine (2 X 10(-5) or 2 X 10(-4) M) did not reverse the specific vasodilating effect of naloxone (3 X 10(-5) M) on norepinephrine-induced constriction. Rather, morphine and naloxone together produced a greater vasodilating effect on norepinephrine-induced constriction than either agent alone. Naloxone (3 X 10(-5) M) failed to alter either phenylephrine-induced constriction or clonidine-induced constriction. The vasodilating effect of naloxone (3 X 10(-5) M) on 10(-3) M norepinephrine-induced constriction was not reduced with 10(-6) M propranolol. These results suggest that the vasodilating effect of naloxone on norepinephrine-induced constriction does not result from an antagonistic action on opiate receptors, direct inhibition of alpha-adrenoreceptors, or direct stimulation of beta-adrenoreceptors in canine cerebral arterial smooth muscle. The vasodilating effect of naloxone on norepinephrine-induced constriction may influence the CBF changes following naloxone administration.
mesh_terms: D000818:Animals; D001488:Basilar Artery / Q000187:drug effects / Q000502:physiology; D004285:Dogs; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D006454:Hemoglobins / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D006454:Hemoglobins; D011941:Receptors, Adrenergic; D012701:Serotonin; D009270:Naloxone; D011189:Potassium Chloride; D009638:Norepinephrine; D004837:Epinephrine