抄録
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 onphasic 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 10times 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 .
