title: The DA1 receptor agonist fenoldopam (SK & F 82526) is also an alpha 2-adrenoceptor antagonist.
abstract: The alpha-adrenoceptor activity of fenoldopam was evaluated in three different in vitro tissue preparations. In rabbit isolated aortic rings fenoldopam displayed weak alpha 1-adrenoceptor antagonist activity (-log KB = 5.41) and displayed no alpha 1-adrenoceptor agonist activity. In contrast, fenoldopam demonstrated moderately potent antagonist properties at the alpha 2-adrenoceptor in two other tissue preparations. In in vitro model systems used for the characterization of alpha 2-adrenoceptors, fenoldopam competitively antagonized the effects of the alpha 2-adrenoceptor agonist B-HT 920. In the dog isolated saphenous vein and in the isolated field-stimulated guinea-pig ileum, fenoldopam antagonized the effects of B-HT 920 with -log KB values of 7.78 and 7.60, respectively. These data indicate that in addition to being an agonist at DA1 receptors, fenoldopam is also a relatively selective antagonist at alpha 2-adrenoceptors.
authors.forename: E H
authors.initials: EH
authors.lastname: Ohlstein
authors.forename: B
authors.initials: B
authors.lastname: Zabko-Potapovich
authors.forename: B A
authors.initials: BA
authors.lastname: Berkowitz
mesh_terms: D000316:Adrenergic alpha-Agonists; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001552:Benzazepines / Q000494:pharmacology*; D004285:Dogs; D004558:Electric Stimulation; D005260:Female; D018818:Fenoldopam; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D011817:Rabbits; D011954:Receptors, Dopamine / Q000187:drug effects*; D012501:Saphenous Vein / Q000187:drug effects; D013154:Spleen / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D000316:Adrenergic alpha-Agonists; D001552:Benzazepines; D011954:Receptors, Dopamine; D014665:Vasodilator Agents; D018818:Fenoldopam