ETA-dependent pressor effects and release of prostacyclin induced by endothelins in pulmonary and renal vasculature.

Abstract

BQ-123, a selective endothelin A (ETA) receptor antagonist, was used to study the receptors involved in the ET-1-induced release of prostacyclin (PGI2) in perfused rat lung and rabbit kidney and the pressor effects of ET-1 in rabbit renal vasculature. In perfused rat lung, infusion of ET-1 (5 nM) significantly increased the release of PGI2, which was markedly reduced after a 15-min infusion of BQ-123 (1 microM). In rabbit kidney, the PGI2 release induced by ET-1 (10 nM) was abolished by a 15-min pretreatment with BQ-123 (1 microM). In both preparations the ET-1-induced release of PGI2 was fully restored 60 min after the interruption of BQ-123 infusion. In rabbit kidney a dose-dependent increase of perfusion pressure was also observed after bolus injections of ET-1 (5 and 10 pmol). The pressor responses to ET-1 were abolished by BQ-123 (0.1 microM), and 60 min after interruption of the infusion of the antagonist, the responses to ET-1 were restored to 68% and 99% of control values, respectively. Two selective ETB receptor agonists, IRL 1620 and BQ-3020, were inactive as pressor and prostanoid-releasing agents at doses and concentration 25-50 times higher than for ET-1 in perfused rabbit kidney. A higher concentration of BQ-123 (1 microM) did not modify the pressor responses to angiotensin II (5 nmol). Our results support the hypothesis that ET-1-induced release of vasodilatory prostanoids from perfused rat lung and rabbit kidney and constriction of rabbit renal vasculature are triggered by activation of ETA receptors.