INCREASED LUNG PREPROET-1 AND DECREASED ETB-RECEPTOR GENE-EXPRESSION IN FETAL PULMONARY-HYPERTENSION

Endothelin (ET)-1, a potent vasoconstrictor and smooth muscle mitogen, is produced from its precursor, preproET-1, by endothelin-converting enzyme (ECE)-1 activity. ET-1 may bind to two receptors, ETA and ETB, that mediate vasoconstriction and vasodilation in the ovine fetal lung , respectively. ET-1 contributes to high pulmonary vascular resistance in experimental perinatal pulmonary hypertension induced by ligation of the ductus arteriosus in the fetal lamb. Physiological studies in t his model have demonstrated enhanced ETA- and diminished ETB-receptor activities and a threefold increase in lung immunoreactive ET-1 protei n content. We hypothesized that increased ET production and an imbalan ce in receptor expression would favor vasoconstriction and smooth musc le cell hypertrophy in pulmonary hypertension and may be partially due to alterations in gene expression. To test this hypothesis, we studie d lung mRNA expression of preproET-1, ECE-1, and the ETA and ETB recep tors in normal and hypertensive fetal lambs. Total RNA was isolated fr om whole lung tissue in normal late-gestation fetuses (135 +/- 3 days; 147 days = term) and from animals with pulmonary hypertension after d uctus arteriosus ligation for 8 days (134 +/- 4 days). Ductus arterios us ligation increased right ventricular hypertrophy [control 0.56 +/- 0.02 vs. hypertension 0.85 +/- 0.05; right ventricle/(left ventricle septum); P < 0.05]. Northern blot analysis was performed using cDNA p robes and was normalized to the signal for 18S rRNA. We found a 71 +/- 24% increase in steady-state preproET-1 mRNA (P < 0.05) and a 62 +/- 5% decrease in ETB mRNA (P < 0.05) expression in ductus arteriosus lig ation. ECE-1 and ETA-receptor mRNA expression did not change. We concl ude that chronic intrauterine pulmonary hypertension after ductus arte riosus ligation increases steady-state preproET-1 mRNA and decreases E TB-receptor mRNA without changing ECE-1 mRNA or ETA-receptor mRNA expr ession. These findings suggest that increased ET-1 production and decr eased ETB-receptor expression may contribute to increased vasoconstric tor tone in this experimental model of neonatal pulmonary hypertension .