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P atients with sickle-cell disease (SCD) suffer from tissue damage and life-threatening complications caused by vasoocclusive crisis (VOC). Endothelin receptors (ETRs) are mediators of one of the most potent vasoconstrictor pathways in mammals, but the relationship between vasoconstriction and VOC is not well understood. We report here that pharmacological inhibition of ETRs prevented hypoxia-induced acute VOC and organ damage in a mouse model of SCD. An in vivo ultrasonographic study of renal hemodynamics showed a substantial increase in endothelin-mediated vascular resistance during hypoxia/reoxygenation-induced VOC. This increase was reversed by administration of the dual ETR antagonist (ETRA) bosentan, which had pleiotropic beneficial effects in vivo. It prevented renal and pulmonary microvascular congestion, systemic inflammation, dense rbc formation, and infiltration of activated neutrophils into tissues with subsequent nitrative stress. Bosentan also prevented death of sickle-cell mice exposed to a severe hypoxic challenge. These findings in mice suggest that ETRA could be a potential new therapy for SCD, as it may prevent acute VOC and limit organ damage in sickle-cell patients.