Effect of morphine on the cat middle cerebral artery.
Morphine (up to 3 X 10(-4) M) elicited concentration-dependent contractions in cat middle cerebral arteries, higher concentrations induced vasodilation. These responses were annulled in the presence of 1-methyl-3-isobutylxanthine, but unaffected by diphenhydramine, cimetidine, phentolamine or naloxone. Ca2+ suppression blocked the morphine-evoked contractions and Ca2+ addition antagonized its vasodilatory effects. Nifedipine induced a marked relaxation in arteries previously contracted with morphine. Preincubation with nifedipine induced a decrease in the contraction elicited by morphine while it increased the vasodilatory phase. Morphine did not produce a significant effect in femoral arteries. In cerebral arteries previously submitted to an active tone, the opioid-induced vasodilation was unchanged by naloxone, cimetidine, diphenhydramine or ouabain, whereas Ca2+ addition antagonized this effect. These results indicate: that the opioid effects are mediated neither by opiate receptors nor by noradrenaline or histamine release; and that an antagonism exists between Ca2+ and the vasodilation caused by morphine.
D000818:Animals; D002415:Cats; D002536:Cerebral Arteries / Q000032:analysis / Q000187:drug effects*; D000242:Cyclic AMP / Q000032:analysis; D005263:Femoral Artery / Q000187:drug effects; D006636:Histamine Release / Q000187:drug effects; D066298:In Vitro Techniques; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000378:metabolism; D011188:Potassium / Q000037:antagonists & inhibitors; D011957:Receptors, Opioid / Q000187:drug effects; D012702:Serotonin Antagonists
D011957:Receptors, Opioid; D012702:Serotonin Antagonists; D009270:Naloxone; D009020:Morphine; D000242:Cyclic AMP; D011188:Potassium; D009638:Norepinephrine