Because endothelin-1 has a potent and long-lasting vasoconstrictive action, it has been proposed that it plays some important roles in the pathogenesis of delayed cerebral vasospasm following subarachnoid hemorrhage. We examined the preventive effect of a novel ETA receptor antagonist, BQ-485, on experimental vasospasm using canine two-hemorrhage model of subarachnoid hemorrhage. The IC50 value of BQ-485 on [125I]endothelin-1 binding was 3.4 x 10(-9) M for ETA receptor and 26 x 10(-6) M for ETB receptor. Systemic continuous administration of 120 mg/day of the agent inhibited the narrowing of canine basilar artery on day 7 following experimental subarachnoid hemorrhage (75.0% vs 59.9% (control), p < 0.01). The present results suggest that endothelin-1 and ETA receptor participate in the pathogenesis of delayed cerebral vasospasm.