Influence of dopamine and noradrenaline on isolated cerebral arteries of the dog.

1 Effects of dopamine and noradrenaline were compared in helically-cut strips of canine cerebral arteries. 2 Dopamine caused a greater maximal contraction than noradrenaline, although the ED50 for noradrenaline was appreciably less. The contraction induced by these amines was reversed to a relaxation by treatment with phenoxybenzamine. 3 Relaxation induced by dopamine in phenoxybenzamine-treated and prostaglandin-contracted cerebral arteries was not influenced by 1 muM propranolol, while relaxation induced by noradrenaline at low concentrations (2 muM and 10 muM) was significantly attenuated. Neither aminophylline nor atropine affected the relaxant effect of dopamine. 4 A mechanism other than beta-adrenergic, cholinergic or adenosine-related appears to be involved in the relaxation elicited by dopamine in cerebral arterial strips.