Evidence for oxygenation-induced endothelin release from isolated lungs of chronically hypoxic rats

Hypoxia augments conversion of big-endothelin-1 and endothelin ET(B) receptor-mediated actions in rat lungs

We have examined the effect of endothelin-1, sarafotoxin-6C, big-endothelin-1 and other agents on perfused lungs from chronically hypoxic rats. Increases in pulmonary perfusion pressure induced by big-endothelin-1, endothelin-1, phenylephrine and potassium chloride were enhanced in hypoxic lungs, while the constrictor action of sarafotoxin-6C was not increased. When basal pulmonary perfusion pressure was raised, low doses of endothelin-1 and sarafotoxin-6C produced decreases in pulmonary perfusion pressure which were significantly greater in chronically hypoxic lungs, whereas responses to sodium nitroprusside were unchanged. Endothelin ET(B) receptor-mediated bronchoconstrictor responses were also potentiated in hypoxic lungs, whereas responses to carbachol were not. In hypoxic lungs, conversion of big-endothelin-1 to endothelin-1 was significantly increased. These data provide evidence for a generalised increase in vasomotor activity in chronically hypoxic lungs, and a more selective increase in endothelin ET(B) receptor-mediated vasodilator and bronchoconstrictor responses. Hypoxia also augments the conversion of big-endothelin-1 to endothelin-1.

Chronic hypoxia differentially alters the responses of pulmonary arteries and veins to endothelin-1 and other agents

The effects of chronic hypoxia on the responses of rat large pulmonary arteries and veins to vasoactive agents have been examined. Endothelin-1-induced contractions of pulmonary arteries and pulmonary veins were reduced by chronic hypoxia. In contrast, chronic hypoxia augmented sarafotoxin 6c-induced contractile responses in pulmonary veins but not in pulmonary arteries. Chronic hypoxia augmented the constrictor effect of phenylephrine in pulmonary arteries, but not in pulmonary veins. The thromboxane receptor agonist, U46619 (9,11-dideoxy-9alpha,11alpha-epoxy-methanoprostaglandin++ + f2alpha) contracted pulmonary arteries and pulmonary veins, and although maximal responses were not altered in chronically hypoxic preparations, the EC50 value in pulmonary arteries was increased following chronic hypoxia. The relaxant effects of acetylcholine and isoprenaline on pulmonary arteries were potentiated by chronic hypoxia. In contrast, ionomycin-mediated relaxations of pulmonary arteries and pulmonary veins were reduced, while sodium nitroprusside-induced relaxation of pulmonary arteries and veins were not altered by chronic hypoxia. Previous studied have looked primarily at the effects of chronic hypoxia on pulmonary arteries. This data provides evidence that chronic hypoxia also causes selective changes in the reactivity of large pulmonary veins.