Loss of endothelium-dependent relaxation in proximal pulmonary arteries from rats exposed to chronic hypoxia: effects of in vivo and in vitro supplementation with L-arginine.

To explore endothelium-dependent relaxation and the L-arginine (L-ARG)-nitric oxide (NO) pathway during chronic hypoxia, we examined isolated rings from large conduit pulmonary arteries and aorta from rats exposed to either room air (N), 3-week hypoxia (H), or 3-week H followed by 72-h recovery to normoxia (room air). We examined the vasodilatory actions of acetylcholine (ACh), ionophore A23187, and endothelin-3 (ET-3) on extrapulmonary left and right branches of pulmonary arteries and thoracic aorta precontracted by phenylephrine (PE 10(-6) M). Endothelium-dependent relaxation of N rat pulmonary arteries and aorta to ACh and A23187 was abolished in the presence of L-NG nitroarginine methyl ester (L-NAME 10(-4) M) or methylene blue (MB 10(-5) M) but was suppressed only partially by NG-monomethyl-L-arginine (L-NMMA 5 x 10(-4) M). In pulmonary arteries but not in aorta, ET-3 induced endothelium-dependent relaxation that was suppressed by L-NAME, MB, and L-NMMA. Pulmonary arteries from H rats did not relax with ET-3. As compared with those of N rats, they exhibited less relaxation to ACh and A23187, (47 +/- 3 vs. 89 +/- 2 and 53 +/- 2 vs. 85 +/- 4%, p < 0.001, respectively) but exhibited similar relaxation to the nonendothelium-dependent vasodilator linsidomine. In contrast, endothelial-relaxation did not differ between N and H rat aorta.2+ pretreatment with L-ARG.