Abstract
Barbiturates in high doses have been used for the protection of the ischemic neurological condition after subarachnoid hemorrhage. The authors examined the pharmacological effects of three kinds of barbiturates (pentobarbital, thiopental, and thiamylal) on isolated canine basilar arteries, measuring the isometric tension of the arteries in vitro and the effects of intravenously administered pentobarbital on an experimentally induced canine angiospasm model, using an angiographic technique. The results obtained were as follows: 1) Barbiturates induced relaxation of canine cerebral vascular strips which had been contracted with high KCI and prostaglandin F2 alpha, in a dose dependent manner. 2) Barbiturates showed non-competitive inhibition of extracellular calcium ions in a preparation treated with high KC1, and the drug inhibited contraction induced by caffeine in a calcium free solution. 3) Systemic administration of the drugs showed no significant vasodilatory action on an experimentally induced spastic artery. An inhibitory action of the barbiturates on contraction of isolated arterial strips in vitro might be due not only to blockage of calcium influx across the cell membranes but also to inhibition of the intracellular calcium ion mobilization. However, in the conventional therapeutic dose, direct action of the agent on the artery can not be expected in the teatment of spastic cerebral artery caused by subarachnoid hemorrhage.
