Upregulation of endothelial nitric oxide synthase and endothelin-1 in pulmonary hypertension secondary to heart failure in aorta-banded rats.

This study assessed alterations in expression of pulmonary endothelial nitric oxide synthase (eNOS) and endothelin-1 (ET-1) in rats with pulmonary hypertension (PH) after the ascending aorta had been banded. Rats were studied 12 weeks after banding, which resulted in left heart failure with elevated pulmonary arterial pressure (banded: 31.3 +/- 5.9 (mean +/- SD) mmHg; sham: 20.0 +/- 4.7 mmHg, P<0.05). Competitive reverse transcription-polymerase chain reaction demonstrated significant increases in pulmonary expression of preproET-1 mRNA and eNOS mRNA. Western blot analysis indicated increased pulmonary eNOS protein. Radioimmunoassays indicated increased plasma ET-1 concentrations in the pulmonary artery (banded: 12.4 +/- 1.5 pg/ml; sham: 9.0 +/- 1.3 pg/ml, P<0.01) and increased ET-1 content in lungs (banded: 240 +/- 21 ng/g protein; sham: 203 +/- 20 ng/g protein, P<0.05). There was increased immunohistochemical staining of eNOS and ET-1 in the pulmonary vascular endothelium of aorta-banded rats. Even in the presence of increased eNOS expression, it was not clear how nitric oxide (NO) production (decreased, unchanged, or increased) was involved in the compensatory mechanism to offset pulmonary vasoconstriction. Increased ET-1 expression may be important in mediating PH secondary to aortic banding, and may offer insights into the use of ET-1 antagonists in treating patients with PH secondary to heart failure.