Effect of nitro-L-arginine on endothelium-dependent hyperpolarizations and relaxations of pig coronary arteries.

1. Endothelium-dependent relaxation is caused by an endothelium-derived relaxing factor (EDRF) identified as nitric oxide (NO). Our objective was to test whether one or several distinct endothelium-dependent relaxing factors exist. 2. In pig coronary arteries, a hyperpolarization accompanied by the relaxation caused by high concentrations of substance P (SP) and bradykinin (BK). 3. To examine the role played by nitric oxide and prostacyclin in the endothelium-dependent relaxations and hyperpolarizations caused by SP and BK on pig coronary arterial strips, the production of NO was inhibited by NG-nitro-L-arginine (L-NNA) and the production of prostacyclin was inhibited by indomethacin, while monitoring smooth muscle membrane potential and isometric tension. 4. Indomethacin had no effect on resting isometric tension nor on SP and BK relaxations of strips precontracted by prostaglandin F2 alpha. 5. L-NNA contracted arterial strips with intact endothelium, without changing the membrane potential of smooth muscles. 6. The inhibitor shifted to the right the concentration-response curve of kinins by 0.2 nM SP and 20 nM BK. It inhibited the maximal relaxations and hyperpolarizations by 30%. 7. The results show that, in pig coronary arteries, EDRF (NO) mainly controls the basal tension, whereas other factor(s) play(s) an important role in hyperpolarizations and relaxations caused by the kinins.