BQ-788 is a selective and potent ETB receptor antagonist with potential hypertensive activity.BQ-788 inhibits ET-1 binding to ETB receptors and inhibits exogenous ET-1-induced elevation of coronary artery perfusion pressure.

ETA:1300 nM (Human SK-N-MC cells), ETB:1.2 nM

BQ-788 potently and competitively inhibits the binding of (125I-labeled ET-1) to ETB receptors in human Girardi heart cells (hGH) with an IC50 of 1.2 nM, but poorly inhibits the binding to ETA receptors in human neuroblastoma cells (SK-N-MC) with an IC50 of 1300 nM. Up to 10 μM, BQ-788 shows no agonistic activity and competitively inhibits vasoconstriction induced by an ETB-selective agonist (pA2, 8.4). Additionally, BQ-788 inhibits several bioactivities of ET-1, including bronchoconstriction, cell proliferation, and clearance of perfused ET-1[1].

In conscious rats, BQ-788 (3 mg/kg/h, i.v.) completely inhibits ETB receptor-mediated depressor responses induced by a pharmacological dose of ET-1 or sarafotoxin6c (0.5 nmol/kg, i.v.), but not pressor responses. Additionally, BQ-788 markedly increases the plasma concentration of ET-1, considered an index of potential ETB receptor blockade in vivo. In Dahl salt-sensitive hypertensive (DS) rats, BQ-788 (3 mg/kg/h, i.v.) raises blood pressure by about 20 mm Hg. It is reported that BQ-788 also inhibits ET-1-induced bronchoconstriction, tumor growth, and lipopolysaccharide-induced organ failure[1]. BQ 788 (3 mg/kg) results in an eightfold leftward shift in the ET-1 dose-response curve, suggesting significant involvement of ETB dilator receptors[2]. In mice treated with 30 nmol BQ-788 by intraplantar administration, there is a reduction in mechanical hyperalgesia (47% and 42%), thermal hyperalgesia (68% and 76%), oedema (50% and 30%), myeloperoxidase activity (64% and 32%), and overt-pain like behaviors. Additionally, intraplantar treatment with clazosentan or BQ-788 decreases spinal (45% and 41%) and peripheral (47% and 47%) superoxide anion production as well as spinal (47% and 47%) and peripheral (33% and 54%) lipid peroxidation, respectively[3].