Dopamine contracted isolated canine coronary arteries at initial concentrations of 5 times 10(-6) mol/l. In the presence of phentolamine or phenoxybenzamine and after contraction of the arteries with K+ or prostaglandin F2alpha, dopamine caused dose-related relaxation at initial concentrations of 5 times 10(-6) mol/l and 10(-6) mol/l. Propranolol, 10(-6) mol/l, and haloperidol, 10(-5) mol/l, did not antagonize the relaxation.
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Toda et al. (1975) studied this question.