Dopamine induced relaxation of isolated canine renal, mesenteric, and femoral arteries contracted with prostaglandin F2-alpha.

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Abstract
The purpose of this investigation was to develop a system for studying the effects of dopamine on isolated blood vessels. Canine renal, mesenteric, and small femoral arteries (less than 1 mm outside diameter) were exposed to phenoxybenzamine 10-5 M for one hour and contracted with prostaglandin F2-alpha. Cumulative concentrations of dopamine ranging from 10-6 to 10-4 M caused dose-related relaxation of the arteries. Propranolol 10-6 M did not affect the relaxation in concentrations which markedly antagonized the effects of isoproterenol. Large femoral arteries (greater than 1 mm outside diameter) did not relax with similar concentrations of dopamine. N-methyldopamine (epinine) produced similar relaxation; 3-methoxytyramine was inactive. Specific antagonism could not be demonstrated by the postulated dopamine antagonists-haloperidol, chlorpromazine, apomorphine, or bulbocapnine-in concentrations up to 10-5 M. Higher concentration of these agents could not be used because they caused the arteries to relax. This study demonstrated that PGF2-alpha-contracted arteries pretreated with phenoxybenzamine are suitable for further investigations of putative dopamine agonists and antagonists.