title: Pharmacological profile of the vascular responses to dopamine in the canine external carotid circulation.
abstract: The present study investigated the effects of dopamine on the canine external carotid circulation. One min. intracarotid artery (i.c.) infusions of dopamine (10-310 microg min.-1) produced dose-dependent decreases in the canine external carotid conductance without affecting blood pressure or heart rate. This effect was mimicked by the D1/2-like receptor agonist apomorphine (1-310 microg min-1), but not by the D2-like receptor agonist, bromocriptine (31-310 microg min.-1). In contrast, fenoldopam (1-310 microg min.-1, intracarotid), a D1-like receptor agonist, produced dose-dependent increases in external carotid conductance. The vasoconstrictor response to dopamine was abolished after intravenous administration of the antagonists, phentolamine (alpha1/2; 2000 microg kg-1) or rauwolscine (alpha2; 100 microg kg-1), but remained unaffected after prazosin (alpha1; 100 microg kg-1) or haloperidol (D2-like; 1000 microg kg-1). Interestingly, after phentolamine not only were the vasoconstrictor responses to dopamine abolished, but even a dose-dependent vasodilator component was unmasked. These vasodilator responses to dopamine remained unchanged after intravenous haloperidol or propranolol (1000 microg kg-1 each). On the other hand, the vasodilator responses to fenoldopam, which remained unchanged after intravenous saline (0.1 ml kg-1), propranolol (1000 microg kg-1) or vagosympathectomy, were abolished by the D1-like receptor antagonist, SCH-23390 (10 microg kg-1). Lastly, the responses to dopamine and fenoldopam were not significantly altered after intraperitoneal pretreatment with reserpine (5 mg kg-1; -24 hr). The above results suggest that the canine external carotid vasoconstrictor responses to dopamine: (i) are mainly mediated by alpha2-adrenoceptors; and (ii) overshadow a vasodilator component, which involves vascular D1-like receptors.
authors.affiliation: Department of Pharmacobiology, CINVESTAV-IPN, Czda. de los Tenorios 235, Col. Granjas-Coapa, 14330 México D.F., México. carlos_villalon@infosel.net.mx
authors.forename: Carlos M
authors.initials: CM
authors.lastname: Villalón
authors.forename: Eduardo
authors.initials: E
authors.lastname: Ramírez-San Juan
authors.forename: Araceli
authors.initials: A
authors.lastname: Sánchez-López
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Bravo
authors.forename: Edwin W
authors.initials: EW
authors.lastname: Willems
authors.forename: Pramod R
authors.initials: PR
authors.lastname: Saxena
authors.forename: David
authors.initials: D
authors.lastname: Centurión
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001552:Benzazepines / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D001971:Bromocriptine / Q000494:pharmacology; D002342:Carotid Artery, External / Q000187:drug effects* / Q000502:physiology; D004285:Dogs; D004298:Dopamine / Q000494:pharmacology* / Q000502:physiology; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D018818:Fenoldopam / Q000494:pharmacology; D006220:Haloperidol / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D014439:Tyramine / Q000494:pharmacology; D014628:Vagotomy; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D001552:Benzazepines; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D001971:Bromocriptine; D018818:Fenoldopam; D006220:Haloperidol; D001058:Apomorphine; D004298:Dopamine; D014439:Tyramine