title: The direct inhibitory action of phentolamine on the contraction of rabbit basilar artery.
abstract: The effects of phentolamine on rabbit basilar artery were studied and compared with those on other smooth muscles. The drug showed a dose-dependent depressing effect on high-potassium-induced contracture of rabbit basilar artery. The depressing effect was stronger on tonic than on phasic contraction. When phentolamine was applied during high-potassium-induced tonic contraction, dose-dependent relaxation was observed. The degree of phentolamine-induced-relaxation of high-potassium-induced tonic contraction was not affected by surgical denervation of the basilar artery, although catecholamine content was almost completely lost, as indicated by chemical and histochemical experiments. The relaxed tension caused by phentolamine was reversed by addition of Ca in a dose-dependent manner. Verapamil also showed a dose-dependent relaxing effect on high-potassium-induced contracture, with this relaxed tension being reversed by the addition of Ca in a dose-dependent manner. The relaxing effect of phentolamine on rabbit basilar artery was stronger than on rabbit aorta or guinea-pig taenia coli. Phentolamine depressed serotonin- or histamine-induced contraction at a concentration more than 10 times higher than the concentration for depression of noradrenaline-induced contraction. The depression of high-potassium-induced contracture and reversal by additional Ca, especially in denervated preparations, indicates that phentolamine acts directly on smooth muscle in a similar manner to that of Ca antagonists.
mesh_terms: D000818:Animals; D001488:Basilar Artery; D002118:Calcium / Q000502:physiology; D002395:Catecholamines / Q000032:analysis; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009412:Nerve Fibers / Q000032:analysis; D010646:Phentolamine / Q000494:pharmacology*; D011817:Rabbits; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002395:Catecholamines; D014700:Verapamil; D002118:Calcium; D010646:Phentolamine