Control of cerebral vasospasm by parenteral phenoxybenzamine

Cerebral vasospasm has been studied in the basilar artery of the cat. The ability of alpha adrenergic blocking agents to prevent and alleviate spasm produced by the application of blood to the basilar artery has been investigated. Parenteral phenoxybenzamine is effective in preventing spasm under these experimental conditions when given in doses of 12 mg/kg provided at least two hours elapse between the administration of the drug and the application of the blood. The drug has been found effective up to 24 hours after parenteral administration. The systemic response to alpha adrenergic blockade and the effects on spasm of the basilar artery produced by different doses at intervals from 1 to 44 hours after the administration of the drug are presented. Although parenteral phenoxybenzamine is effctive in preventing spasm from subarachnoid blood, it does not prevent spasm from mechanical manipulation of the vessels. This would indicate that mechanisms other than adrenergic stimulation itself may be operative in cerebral vasospasm. The alteration of spasm from blood and mechanical manipulation by other alpha adrenergic blocking agents has been studied and the possible modes of action of these drugs are discussed.