The ETA receptor antagonist, BMS-182874, reduces acute hypoxic pulmonary hypertension in pigs in vivo

Objective: Elevated levels of the potent vasoactive peptide endothelin (ET), have been found in pathophysiological conditions associated with pulmonary hypertension. In this study, we have investigated the effects of the ETA receptor antagonist, BMS-182874, on hypoxic pulmonary hypertension in pigs. Methods: Pigs were subjected to acute, intermittent 15-min periods of hypoxia (FiO(2) 0.1). Following a first hypoxia establishing hypoxic baseline values, vehicle or EMS-182874 (10 or 30 mg/kg) was administered i.v. before a second hypoxic period. In separate groups of animals, the effects of the nitric oxide synthase inhibitor N-omega-nitro-L-arginine (L-NNA) in combination with EMS-182874 (10 mg) during repeated hypoxia were investigated. The ET-1-blocking properties of EMS-182874 were studied in vivo by infusion of ET-1 during normoxia and in vitro using isolated porcine pulmonary arteries. Results: The hypoxia-evoked increase in mean pulmonary artery pressure was reduced by administration of EMS-182874 (10 mg/kg i.v.; from 42 +/- 8 to 34 +/- 4 mmHg, P < 0.05 and 30 mg/kg i.v.; from 38 +/- 4 to 30 +/- 5 mmHg, P < 0.05). In addition, EMS-182874 at 30 mg/kg reduced the pulmonary vascular resistance during hypoxia (from 7.4 +/- 1.5 to 5.3 +/- 1.1 mmHg.min.l(-1) P < 0.05). The hemodynamic response to repeated hypoxia was reproducible in control animals and unaffected by the cyclo-oxygenase inhibitor diclophenac (3 mg/kg). Infusion of L-NNA alone resulted in an augmented pulmonary vasoconstriction during hypoxia: pulmonary arterial pressure from 35 +/- 6 to 43 +/- 9 mmHg; P < 0.05 and vascular resistance from 7.2 +/- 1.1 to 9.9 +/- 1.8 mmHg.min.l(-1); P < 0.05. L-NNA in combination with BMS-182874 (10 mg/kg) resulted in a hypoxic pulmonary vasoconstriction of similar magnitude as hypoxic baseline. In addition, EMS-182874 reduced the hemodynamic response to ET-1 in normoxic pigs and competitively antagonized the vasoconstrictor effect of ET-1 in isolated porcine pulmonary arteries. Conclusions: The non-peptide, selective ETA receptor antagonist, BMS-182874, reduces hypoxic pulmonary vasoconstriction in pigs. The reduction in pulmonary vascular response to hypoxia following BMS-182874 is at least partly independent of nitric oxide. (C) 1998 Elsevier Science B.V.