Further investigations of the central effects of a calcum-entry blocker [Verapamil]

ABSTRACT

The intracerebroventricular injection [ICVI] of the selective alpha2- agonist clonidine into anesthetized rabbits produced significant lowering in mean arterial blood pressure [B.P]. However, each of the entry selective - anatagonist yohimbine and the Ca2+ entry blocking agent verapamil produced transient increase in B.P. Pretreatment with yohimbine completely prevented the occurrence of the hypotensive effect of the subsequent dose of clonidine. Similarly, prior administration of verapamil, significantly attenuated clonidine-hypotensive effect. Both yohimbine and verapamil displayed considerable prophylactic activity against ouabain-induced arrhythmias in conscious mice. These results support the suggestion that alpha2- adrenoceptors play a role in the cardiovascular responses of Ca2+ - entry blockers. Verapamil injected intracerebroventricularly but not yothimbine, displayed protective capacity against neurological changes, including the convulsions, induced by central injection of ouabain into conscious mice. These results reflect the wide spectrum of the CNS actions of Ca2+ - entry blocker verapamil compared to those of alpha2- antagonists