Effects of dopamine on the conductance of perfused vascular beds of the chloralosed cat.

1. Dopamine produced vasoconstriction followed by secondary vasodilatation in the perfused cat hindquarters and splanchnic region. Low doses produced only vasodilatation in the splanchnic region.2. Phenoxybenzamine abolished, while despiramine and cocaine potentiated, the vasoconstrictor and secondary dilator actions of dopamine.3. After phenoxybenzamine, dopamine produced only vasodilatation in both the hindquarters and splanchnic region, being more effective in the latter.4. Haloperidol, but not propranolol, atropine or mepyramine, antagonized dopamine-induced vasodilatation.5. Dopamine differs from other catecholamines in that, while its cardiac effects are mediated by a beta-adrenoceptive mechanism, its vasodilator effects are not.6. The results support the concept of a specific receptor mediating dopamine vasodilatation.