Effects of Naloxone on Canine Cerebral Vascular Smooth Muscle

• Published in: Journal of cerebral blood flow and metabolism 1984-06, Vol.4 (2), p.166-172
• Main Authors: Sasaki, Tomio, Kassell, Neal F., Turner, Donn M., Maixner, William, Torner, James C., Coester, Hans C.
• Format: Article
• Language: English
• Subjects: Animals; Basilar Artery - drug effects; Basilar Artery - physiology; Dogs; Epinephrine - pharmacology; Female; Hemoglobins - pharmacology; Male; Muscle, Smooth, Vascular - drug effects; Naloxone - pharmacology; Norepinephrine - pharmacology; Potassium Chloride - pharmacology; Receptors, Adrenergic - drug effects; Serotonin - pharmacology; Vasoconstriction - drug effects; Vasodilation - drug effects
• ISSN: 0271-678X; 1559-7016
• DOI: 10.1038/jcbfm.1984.24

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 × 10−4 M) it produced nonspecific vasodilation, and (2) at lower concentrations (3 × 10−7, 3 × 10−6, and 3 × 10−5 M) it inhibited the vasoconstrictor effects of norepinephrine without altering KCl-, serotonin-, or hemoglobin-induced constriction. Morphine (2 × 10−5 or 2 × 10−4 M) did not reverse the specific vasodilating effect of naloxone (3 × 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 × 10−5M) failed to alter either phenylephrine-induced constriction or clonidine-induced constriction. The vasodilating effect of naloxone (3 × 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 α-adrenoreceptors, or direct stimulation of β-adrenoreceptors in canine cerebral arterial smooth muscle. The vasodilating effect of naloxone on norepinephrine-induced constriction may influence the CBF changes following naloxone administration.