Hypoxia-Induced Contractions of Porcine Pulmonary Artery Strips Depend on Intact Endothelium

Abstract

Whether intact endothelium is required for hypoxia-induced contractions of pulmonary vascular muscle in vitro was investigated. Pairs of transverse strips were cut from main pulmonary arteries of pigs, the endothelium from 1 strip was removed and the strips were mounted on force transducers in separate tissue baths. After an adaptation period of 4-6 h at an oxygen tension of 40 torr, strips with intact endothelium contracted spontaneously when the oxygen tension was decreased from 140 torr to near O torr (6.5 .+-. 1.1 gm-wt/cm2, mean .+-. SEM) whereas strips without endothelium contracted significantly less (1.0 .+-. 0.3 gm-wt/cm2, P < 0.001, n = 14 pairs). Strips with and without endothelium contracted equally in response to incremental concentrations of norepinephrine. Each of several drugs (atropine, propranolol, phentolamine, or indomethacin, each 10-5 M) had no effect on hypoxia-induced contractions when added to the bath prior to hypoxia. A decrease in bath pH from 7.4 to 7.2 had no effect. Because the endothelium might be releasing a mediator causing increased tone in response to hypoxia, the bath was cleansed during hypoxia, but this did not change hypoxia-induced contractions. Placing strips with intact endothelium close to strips without endothelium and measuring tension in the bath during hypoxia did not induce contractions in the strip without endothelium. Evidently, an intact endothelium is necessary for hypoxia-induced contractions in vitro in main pulmonary arteries from pigs. Although main pulmonary arteries are not primarily responsible for hypoxic vasoconstriction in vivo, endothelium may have a possible role in the pulmonary vascular response to hypoxia.