INFLUENCE OF DOPAMINE AND NORADRENALINE ON ISOLATED CEREBRAL ARTERIES OF THE DOG

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Abstract
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 μm propranolol, while relaxation induced by noradrenaline at low concentrations (2 μm and 10 μm) was significantly attenuated. Neither aminophylline nor atropine affected the relaxant effect of dopamine. 4 A mechanism other than β-adrenergic, cholinergic or adenosine-related appears to be involved in the relaxation elicited by dopamine in cerebral arterial strips.