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 μg 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 μg min-1), but not by the D2-like receptor agonist, bromocriptine (31-310 μg min.-1). In contrast, fenoldopam (1-310 μg 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 (α1/2; 2000 μg kg-1) or rauwolscine (α2; 100 μg kg-1), but remained unaffected after prazosin (α1; 100 μg kg-1) or haloperidol (D2-like; 1000 μg 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 μg 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 μg kg-1) or vagosympathectomy, were abolished by the D1-like receptor antagonist, SCH-23390 (10 μg 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 α2-adrenoceptors; and (ii) overshadow a vasodilator component, which involves vascular D1-like receptors.,
Pharmacoloy & Toxicology
Department of Pharmacology

Villalón, C., Ramírez-San Juan, E., Sánchez-López, A., Bravo, G., Willems, E., Saxena, P. R., & Centurion, D. (2003). Pharmacological profile of the vascular responses to dopamine in the canine external carotid circulation. Pharmacoloy & Toxicology, 92(4), 165–172. doi:10.1034/j.1600-0773.2003.920406.x