Release of 6-nitrodopamine from human popliteal artery and vein

6-Nitrodopamine (6-ND) is a novel catecholamine that is released from human umbilical cord vessels, and it causes vascular relaxation by acting as a dopamine D₂-receptor antagonist. Here it was investigated whether human peripheral vessels obtained from patients who have undergone surgery for leg amputation release 6-ND, and its action in these tissues. Popliteal artery and vein strips present basal release of 6-ND, as measured by liquid chromatography coupled to tandem mass spectrometry. The release was significantly reduced when the tissues were pre-treated with the nitric oxide synthase inhibitor L-NAME (100 μM), or when the endothelium was mechanically removed. In U-46619 (3 nM) pre-contracted rings, 6-ND induced concentration-dependent relaxations (pEC50 8.18 ± 0.05 and 8.40 ± 0.08, in artery and vein rings, respectively). The concentration-dependent relaxations induced by 6-ND were unaffected in tissues pre-treated with L-NAME, but significantly reduced in tissues where the endothelium has been mechanically removed. In U-46619 (3 nM) pre-contracted rings, the selective dopamine D₂ receptor antagonist L-741,626 also caused concentration-dependent relaxations (pEC₅₀ 8.92 ± 0.22 and 8.79 ± 0.19, in artery and vein rings, respectively). The concentration-dependent relaxations induced by L-741,626 were unaffected in tissues pre-treated with L-NAME, but significantly reduced in tissues where the endothelium has been mechanically removed. This is the first demonstration that 6-nitrodopamine is released from human peripheral artery and vein rings. The results also indicate that endothelium-derived dopamine is a major contractile agent in the popliteal artery and vein, and that selective dopamine D₂-receptor antagonists such as 6-ND, may have therapeutic potential in the treatment of human peripheral vascular diseases.