Droperidol, its alpha-adrenergic blocking action on the aortic strip and inhibitory action on norepinephrine uptake of the adrenergic terminal of the left atrial strip of rabbit.

In aortic strips, the dose-response curves for phenylephrine were obtained before and after addition of droperidol. Droperidol caused a parallel shift of the curves dose-dependently toward the right side and its grade of the shift was greater than caused by phentolamine at the same concentration. In the left atrial strip, the potentiation of contraction by tyramine was markedly depressed by droperidol. In the reserpinized preparation, the effect of tyramine was depressed markedly and there was no norepinephrine fluorescence. After incubation with norepinephrine they were restored to the same level as in non-reserpinized preparations. However, incubation with droperidol before norepinephrine blocked the restoration. It is postulated that droperidol may have both alpha-adrenergic blocking action and inhibitory action on norepinephrine uptake by adrenergic terminals.