[Effect of phentolamine on cerebral circulation]

The influence of phentolamine hydrochloride on the volumentric circulation rate of the cerebral blood flow, the tone of the cerebral vessels and oxygen tension in the cerebral tissue was studied in acute experiments on anesthetized and nonanesthetized cats. Injected intravenously, phentolamine hydrochloride was found to lower the intra- and extracranial vessels for a long time, the latter to a greater extent. The circulation rate of the cerebral blood flow decreased under conditions of a significant hypotension caused by phentolamine hydrochloride and increased with a stable perfused pressure; pO2 changes in the cerebral tissue corresponded mostly to the blood flow. Preliminary atropinization of the animals and denervation of the carotid regions failed to influence the effect of phentolamine hydrochloride. The latter decreased or prevented the vasoconstrictor action of norepinephrine and phenylephrine hydrochloride (mesatone) on the cerebral vessels.