The variable effects of dopamine among human isolated arteries commonly used for coronary bypass grafts.

UNLABELLED: The direct actions of dopamine on human arterial coronary bypass grafts are not well known. We investigated its effects on isolated rings cut from radial arteries (RA), gastroepiploic arteries (GEA), and internal mammary arteries (IMA) harvested from patients undergoing coronary artery bypass surgery. Dopamine produced dose-dependent contractile responses in RA, an effect independent of the presence of a functional endothelium. The contractions were enhanced by the dopamine A(1) (DA(1))-receptor antagonist SCH23390, whereas they were blocked by an alpha(1)-adrenergic antagonist, prazosin. Results qualitatively similar to these were obtained in both GEA and IMA, although the contractile responses were far smaller. In RA, DA enhanced the norepinephrine (NE)-induced contraction, and this action of dopamine was enhanced by SCH23390. In GEA, small concentrations (<10(-7) mol/L) of DA attenuated the NE-induced contraction but larger concentrations did not. In IMA, DA induced a vasorelaxation on the NE-contraction only at higher concentrations (10(-6)-10(-5) mol/L). In both GEA and IMA, the dopamine-induced vasorelaxations on the NE contraction were completely inhibited by SCH23390. These results suggest that the affinities of DA for DA(1)- and alpha(1)-adrenergic receptors may explain its variable contractile and vasorelaxant effects among these arteries. IMPLICATIONS: Differing affinities of dopamine for dopamine A(1)- and alpha(1)-adrenergic receptors may lead to it having variable contractile and vasorelaxant effects among the arteries supplying grafts for coronary bypass surgery.