Alteration of experimental cerebral vasospasm by adrenergic blockade

✓ Two alpha adrenergic blocking agents have been used to alleviate spasm induced in the basilar artery of the cat by the application of blood or by mechanical manipulation. Parenteral phenoxybenzamine is effective in preventing spasm from blood when given in doses of 6 mg/kg or more provided at least 1½ hours have elapsed between the completion of the infusion and the application of the blood; it also relieves and prevents spasm from blood when applied topically. Phenoxybenzamine does not prevent or alleviate spasm induced by mechanical manipulation of the basilar artery. Phentolamine alleviates both types of spasm, but its effect lasts no more than 15 minutes. The possible modes of action of these drugs are discussed.