Dopamine antagonist effect of verapamil on isolated perfused rabbit ear artery

Rabbit ear arteries were isolated and perfused with Krebs-bicarbonate solution. Brief periods of supramaximal nerve stimulation caused reproducible constriction of the arteries, which was inhibited by dopamine at concentrations ranging from 3.3 X 10(-9) to 3.3 X 10(-7) M. The inhibitory effect of dopamine was antagonized by sulpiride and by verapamil. The dose-response curve to dopamine was shifted to the right by both sulpiride and verapamil, indicative of competitive inhibition. The dopamine antagonist activity of verapamil does not appear to be a consequence of its Ca++ channel inhibitory activity because other calcium antagonists (e.g., nitrendipine and diltiazem) had no similar action.