title: The effects of naloxone on canine splanchnic arterial smooth muscle.
abstract: The pharmacological properties of naloxone on vascular smooth muscle in vitro were examined using canine mesenteric arterial segments. Naloxone exerted two different effects on the artery: (A) naloxone at a high concentration (3 X 10(-4) M) produced a nonspecific vasodilation; and (B) naloxone at lower concentrations (3 X 10(-7), 3 X 10(-6), and 3 X 10(-5) M) augmented the vasoconstrictor effects of epinephrine and norepinephrine without altering KCl- or serotonin-induced constriction. Naloxone's augmenting effect on epinephrine-induced constriction was dose dependent. Even when the arterial strips were incubated in low calcium (0.8 mM) or calcium free Kreb's solution, naloxone (3 X 10(-5) M) still augmented epinephrine-induced constriction. With respect to naloxone's effect on another alpha-adrenoreceptor agonist, naloxone (3 X 10(-5) M) failed to alter phenylephrine-induced constriction. Naloxone's augmenting effect on norepinephrine-induced constriction was abolished when the specimens were incubated with 10(-5) M normetanephrine, while naloxone (3 X 10(-5) M) still augmented the constriction even when the specimens were incubated with 10(-5) M cocaine. These results suggest that naloxone at lower concentrations may augment the constrictor responses to catecholamines, at least in part, by inhibiting the extraneuronal uptake of those catecholamines.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology; D004285:Dogs; D004347:Drug Interactions; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D008297:Male; D008638:Mesenteric Arteries; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D009270:Naloxone / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects
chemical_list: D012701:Serotonin; D009270:Naloxone; D011189:Potassium Chloride; D003042:Cocaine; D002118:Calcium; D009638:Norepinephrine; D004837:Epinephrine