Difference in endothelium-derived hyperpolarizing factor-mediated hyperpolarization and nitric oxide release between human internal mammary artery and saphenous vein

Background-The greater nitric oxide (NO) release that occurs in the interna l mammary artery (IMA) when compared with the saphenous vein (SV) has been suggested by more endothelium-dependent relaxation in the IMA or measured b y bioassay; however, no direct measurement of NO- or endothelium-derived hy perpolarizing factor (EDHF)-mediated hyperpolarization has been reported. T he present study measured such hyperpolarization, as well as NO release, in these vessels. Methods and Results-IMA (n=46) and SV (n=61) segments taken from patients u ndergoing coronary surgery were studied in the organ chamber. Hyperpolariza tion (by intracellular glass microelectrode) and NO release (by NO-sensitiv e electrode) in response to acetylcholine and bradykinin, with and without incubation with N-G-nitro-L-arginine, indomethacin, and oxyhemoglobin, were measured. The resting membrane potential of the smooth muscle cells from t he IMA (58+/-0.8 mV; n=15) was higher than that in those from the SV (-62+/ -0.9 mV; n=23; P=0.0001). The EDHF-mediated hyperpolarization induced by ac etylcholine (10(-5) mol/L: -9.4+/-1.5 mV in IMA, n=10, versus -4.5+/-1.0 mV in SV, n=17; P<0.01) and bradykinin (10(-7) mol/L: -10.9+/-1.5 mV in IMA, n=8, versus -5.1+/-0.5 mV in SV, n=8; P<0.01) and the basal release of NO ( 16.8+/-1.6 nmol/L in IMA, n=13, versus 9.9+/-2.8 nmol/L in SV, n=13; P<0.00 1) were significantly greater in the IMA than in the SV, The duration of ac etylcholine- and bradykinin-induced NO release was longer in the IMA than i n the SV. Conclusions-The basal release of NO and EDHF-mediated hyperpolarization wer e significantly greater in the IMA than in the SV. In addition, the duratio n of the stimulated release of NO was longer in the IMA than in the SV, The se differences may contribute to the superior long-term patency of IMA graf ts.