Dopamine responses in veins, arteries and experimental vein bypass grafts

Background: Dopamine is a commonly used inotropic agent during coronary artery surgery and in the medical therapy of a previously revascularized patient. This study examines in vitro dopamine mediated responses in experimental vein grafts, jugular veins and carotid arteries of the rabbit. The in vitro isometric tension responses to dopamine of 28 days old, common carotid external jugular vein bypass grafts (VG) in New Zealand White rabbits were determined and these responses were compared to those obtained in the external jugular vein (JV) and in the common carotid artery (CA) in the presence and absence of alpha adrenergic blockade. Both endothelialized and de-endothelialized vessels were precontracted with prostagiandin F_2α. Results: Each vessel had a biphasic response to dopamine with relaxation followed by contraction (JV = CA≫VG, Table). After removal of the endothelium, the IC₅₀ of the dopamine mediated relaxation of the VG was significantly enhanced and was greater than either the JV or the CA. Relaxation mediated by dopamine in the JV was unchanged, while that in the CA was significantly decreased. Alpha adrenergic inhibition enhanced dopamine responses in JV, decreased responses in CA but did not alter the responses in the VG. With alpha adrenergic blockade, the responses to dopamine were JV≫VG=CA Jugular Vein Vein Graft Carotid Artery Control 7.86±0.08 6.62±0.22 * 1 7.89±0.47 Denuded 7.82±0.15 8.91±0.09 ** 2 1 7.13±0.15 * Phenoxybeniamine(10^-5M) 8.53±0.08 * 2 6.73±0.56 6.42±0.23 Values are the -log₁₀[IC₅₀], mean±s.e.m. * p<0.05, ** p<0.001 compared to JV 1 p<0.05, 2 p<0.01 compared to CA by ANOVA with post hoc Tukey-Kramer testing. Conclusion: Vein grafts demonstrate markedly different dopamine responses to the JV or the recipient CA. The presence of endothelium significantly inhibits the dopamine response in VG. This study suggests that vein grafts respond uniquely to the vascular agonist dopamine and that this response is mediated in part by the endothelium.