Propranolol Blocks Cocaine-Induced Potentiation of the Contraction in the Smooth Muscle of the Rat Vas Deferens

In the smooth muscle of the rat vas deferens, 10-5M cocaine shifted the dose-response curve to norepinephrine to the left and enhanced the maximal contractions to norepinephrine and methacholine. Propranolol at 10-4M almost completely blocked these potentiating effects of cocaine. Sotalol or lidocaine at 10-4M did not block the potentiating action of cocaine. The cocaine-induced enhancement of the methacholine contraction and its blockade by propranolol was observed in the dibenaminetreated vas deferens. Propranolol also blocked the depolarization-induced enhancement of the methacholine contraction. Together with the previous study demonstrating the calcium-antagonist action for propranolol, these results suggest that propranolol blocks the cocaine-induced enhancement by inhibiting the calcium influx through the potential-dependent calcium channel in the rat vas deferens.