Antagonism by droperidol of dopamine-induced relaxation in isolated dog arteries.

Dopamine caused a dose-related relaxation in helically cut strips of dog coronary and renal arteries treated with phenoxybenzamine andcontracted with prostaglandin F2 alpha. The dose-response curve to dopamine was shifted to the right by droperidol in concentrations above 3 X 10(-5) M. Adenosine-induced relaxations were not attenuated by droperidol. The dose--relaxation curve to isoproterenol was also shifted to the right by droperidol. Propranolol (10(-6) M) failed to significantly alter the dose response curve to dopamine, and in propranolol-treated preparations the antagonism by droperidol of dopamine actions was practically identical with that in control preparations. Droperidol appears to act as a reversible, surmountable antagonist to dopamine actions on dog arterial smooth muscles, and such evidence supports the hypothesis of specific dopamine receptors in dog arteries.