ENHANCED ENDOTHELIN-1 AND ENDOTHELIN RECEPTOR GENE-EXPRESSION IN CHRONIC HYPOXIA

To test the hypothesis that endothelin (ET)-1 synthesis and ET receptor levels are increased selectively in the lung of rats with chronic hypoxic pulmonary hypertension, the current study examined the effects of exposure to chronic hypoxia (10% O-2, 1 atm, 4 wk) on pulmonary arterial pressure, ET-1 levels in plasma and lung, and ET-1 and ET(A) and ET(B) receptor mRNA levels in lung, heart, pulmonary artery, aorta, kidney, spleen, and liver. Hypoxic exposure was associated with increases in pulmonary arterial pressure, plasma ET-1 levels, ET-1 mRNA in lung and pulmonary artery, and ET-1 stores and ET(A) and ET(B) receptor mRNA levels in lung. In thoracic aorta and the four heart chambers, ET(A) and ET(B) receptor mRNA levels were increased, but ET-1 mRNA levels were unchanged from air control levels. No change in ET-1 or ET receptor mRNA levels was seen in organs perfused by the systemic vascular bed, except in liver, where ET(A) receptor mRNA levels were decreased. The findings of concomitant increases in gene transcript levels for ET-1 and the ET(A) and ET(B) receptors in lung, but not in the great vessels or any other organ examined, are consistent with the hypothesis that increased ET-1 synthesis in the lung contributes to pulmonary vascular remodeling and the maintenance of chronic hypoxic pulmonary hy pertension.