Role of NO and EDHF-mediated endothelial function in the porcine pulmonary circulation: Comparison between pulmonary artery and vein

ObjectiveTo compare electrophysiological measurement of nitric oxide (NO) release and endothelium-derived hyperpolarizing factor (EDHF)-mediated endothelial function in porcine pulmonary arteries and veins.MethodsIsolated pulmonary interlobular arteries (PA) and veins (PV) were obtained from a local slaughterhouse. By using a NO-specific electrode and a conventional intracellular microelectrode, the amount of NO released from endothelial cells and hyperpolarization of smooth muscle cells were investigated. The bradykinin (BK)-induced relaxation in the precontraction by U46619 was examined in the absence or presence of NG-nitro-l-arginine (l-NNA), indomethacin (INDO) plus oxyhemoglobin (HbO).ResultsThe basal release of NO was 7.0 ± 1.2 nmol/L in PA (n = 8) and 5.5 ± 1.6 nmol/L in PV (n = 8, p < 0.01). BK-induced release of NO was 160.4 ± 10.3 nmol/L in PA (n = 8) and 103.0 ± 14.7 nmol/L in PV (n = 8, p < 0.001) with longer releasing duration in PA than in PV (14.3 ± 1.3 vs. 12.1 ± 0.8 min, p < 0.01). BK evoked an endothelium-dependent hyperpolarization and relaxation that were reduced by l-NNA, INDO, and HbO (hyperpolarization: 12.8 ± 1.3 vs. 8.0 ± 1.4 mV in PA, n = 6, p < 0.001 and 8.3 ± 1.4 vs. 3.0 ± 0.8 mV in PV, n = 6, p < 0.001; relaxation: 92.8 ± 3.1% vs. 19.6 ± 11.1% in PA n = 8, p < 0.001 and 70.3 ± 7.9% vs. 6.0 ± 6.8% in PV, n = 8, p < 0.001). Both hyperpolarization (8.0 ± 1.4 vs. 3.0 ± 0.8 mV, p < 0.001) and relaxation (19.6 ± 11.1% vs. 6.0 ± 6.8%, p < 0.01) were greater in PA than in PV.ConclusionsBoth NO and EDHF play an important role in regulation of porcine pulmonary arterial and venous tones. The more significant role of NO and EDHF is revealed in pulmonary arteries than in veins.