The orally active nonpeptide selective endothelin ETA receptor antagonist YM598 prevents and reverses the development of pulmonary hypertension in monocrotaline-treated rats.

We investigated the preventive and therapeutic effects of the selective endothelin ETA receptor antagonist potassium(E)-N-[6-methoxy-5-(2-methoxyphenoxy)-2-(pyrimidin-2-yl)pyrimidin-4-yl]-2-phenylenthenesulfonamidate (YM598) on the development of pulmonary hypertension in monocrotaline-induced pulmonary hypertensive and hypoxemic rats. In the prevention study, oral administration of YM598 (0.1 and 1 mg/kg) or bosentan (30 mg/kg) for 4 weeks was started on the day following monocrotaline (60 mg/kg) injection. In the therapeutic study, oral administration of YM598 (0.1, 0.3 and 1 mg/kg) for 2 weeks was started 3 weeks after monocrotaline injection. In the prevention study, a marked increase in pulmonary arterial pressure and right ventricular hypertrophy, a decrease in right cardiac function and hypoxemia were observed. Histopathological examination indicated the presence of pulmonary remodeling, including medial wall thickening of the pulmonary microvasculature and alveolar disorders. YM598 suppressed the increase in pulmonary arterial pressure, right ventricular hypertrophy and systemic congestion, and improved the hypoxemia, but bosentan had only modest effects. Histopathological disorders were also ameliorated by YM598. In the therapeutic study, YM598 also ameliorated the pulmonary hypertension and hypoxemia in monocrotaline-treated rats. These results suggest that YM598 effectively prevented and reversed the development of pulmonary hypertension, and reduced the pulmonary vascular remodeling and parenchymal injury in monocrotaline-treated rats. YM598 also improved hypoxemia which accompanied with the severe pulmonary hypertension in these rats.