Hypotensive and regional haemodynamic effects of fenoldopam and quinpirole in the anaesthetized rat.

The effects of systemic administration of the selective dopamine1 receptor agonist fenoldopam and the selective dopamine2 receptor agonist quinpirole on blood pressure and regional haemodynamics were investigated in anaesthetized normotensive Wistar rats. Both compounds produced dose-dependent reductions in blood pressure. Mesenteric and renal blood flow were enhanced by fenoldopam, but reduced by quinpirole. Hindquarter blood flow was not modified by fenoldopam, but was increased by quinpirole. The calculated vascular resistances were reduced by both compounds in the three vascular beds. The effects of fenoldopam were antagonized by SCH 23390 but SCH 23390 did not affect those of quinpirole. The effects of quinpirole, but not those of fenoldopam, were antagonized by domperidone. Hexamethonium abolished the effects of quinpirole without affecting those of fenoldopam. These results indicate that the hypotensive effects of fenoldopam and quinpirole are due to stimulation of postsynaptic dopamine1 and neuronal dopamine2 receptors, respectively, resulting in differential regional haemodynamic effects.