Experimental assessment of phenoxybenzamine in cerebral vasospasm

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Abstract
The effect of phenoxybenzamine (PBZ) on cerebral vasospasm of the basilar artery induced by the injection of 2 ml of blood into the cisterna magna of dogs was assessed in chronic experiments. The presence of vasospasm was documented arteriographically. In 1 group of animals, 12 mg/kg of PBZ was given i.v. 2 h before the intracisternal injection of blood to ascertain whether this drug prevents the development of vasospasm for 24 h. In another group of animals a 10-2M solution of PBZ was given intracisternally 15 min after vasospasm was produced, and again 24 h afterward, to determine if the drug would reverse an existing spasm. These drug-treated animals were compared with controls which were treated with saline alone. The drug treatment apparently was not statistically superior to saline in any of the groups studied. The finding that saline injected into the cisterna magna reversed the cerebral vasospasm illustrates the importance of this procedure in evaluating effectiveness of drugs and confirms the original observation that washing the CSF with saline can terminate an experimentally induced vasospasm. The fact that intracisternal injections of saline were more effective when given soon after establishment of vasospasm than when injected 24 h afterward supports the conclusion that the pathogenesis of cerebral vasospasm changes with time. The presence of cerebral vasospasm in some animals apparently did not prevent the return of normal behavior.