Droperidol interacts with vascular serotonin receptors and alpha-adrenoceptors

This investigation was performed to determine whether droperidol interacts with 5-hydroxytryptamine (serotonin) receptors in the rat aorta. Droperidol caused concentration-dependent vasorelaxation in endothelium-intact and endothelium-denuded aortic rings precontracted with noradrenaline or 5-hydroxytryptamine. Conversely, the contractile effect of prostaglandin F2 alpha was not affected by droperidol. Pretreatment with propranolol, brompheniramine and atropine (10(-6) M each) did not alter the relaxant effects of droperidol. In addition, droperidol shifted the 5-hydroxytryptamine and noradrenaline concentration-response curves to the right in an apparently competitive manner. However, prazosin did not modify the concentration-response curve to 5-hydroxytryptamine, which is consistent with the hypothesis that the latter has an intrinsic efficacy for non-alpha 1-adrenoceptors. These results strongly suggest that a direct arterial endothelium-independent relaxant action of droperidol can be attributed to a 5-hydroxytryptamine receptor-blocking property and support its vascular alpha-adrenoceptor-blocking effect.