A comparison of the effects of verapamil and cinnarizine upon responses elicited by selective alpha 1- and alpha 2-adrenoceptor agonists in the autoperfused canine hindlimb.

In an attempt to extend the hypothesis that activation of vascular postsynaptic alpha 2-adrenoceptors requires an influx of Ca2+ ions, the effects of 2 calcium entry blocking drugs verapamil and cinnarizine have been examined as inhibitors of the pressor responses to methoxamine and B-HT 920 in autoperfused dog hindlimb preparations. Verapamil (0.1-1 mg i.a.) selectively antagonized responses to B-HT 920 and had little or no effect upon responses to methoxamine, thus supporting this hypothesis. However cinnarizine, over the dose range studied (0.1-1 mg/kg i.a.) produced quantitatively similar inhibitions of the hindlimb responses to B-HT 920 and methoxamine. These results suggest that cinnarizine may have a different site of action to verapamil in resistance vessels of the dog hindlimb.