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BQ-788, ETb Receptor Antagonist

Ishikawo et al1 reported that BQ-788 [N-cis-2, 6- dimethylpiperidinocarbonyl - L-gamma- methylleucyl-D-I- methoxycorbonyltryptophanyl- D-norleucine] to be a potent and competitive inhibitor of 125I-ET-1 binding to ETB receptors on human Girardi heart cells (IC50, 1.2 nM) but only a poor inhibitor of the ET-1 binding to ETA receptors on human neuroblastoma cell line SK-N-MC cells (IC50, 1300 nM). On the basis of a recent study using BQ-123 (ETA receptor antagonist) and BQ-788 (ETB receptor antagonist) to investigate which of the ET receptor subtypes (ETA or ErB) participate in the rapid clearance of endothelin from circulation, Fukuroda et al2 have concluded that ETB receptors play an important role in the clearance of ET-1. Fukurodo et al report that in the rabbit isolated pulmonary artery only a combination of BQ-123 and BQ-788 completely inhibited the contractions induced by I nM ET-1, but the two receptor antagonists individually did not inhibit the contractile action of ET-1. The authors concluded that the activation of either ETA or ETB receptors is sufficient to elicit ET-1 induced contraction, and blockade of both receptor subtypes would be necessary for the inhibition of some ETA/ETB composite types of responses. Doleansjuste has used BQ-123 and BQ-788 to characterize the receptors responsible for ET-I induced release of thromboxane A (2) from the guinea pig lung and endothelium-derived nitric oxide from the rabbit perf used kidney. The effects of BQ-788 on isolated blood vessel and small intestine were studied using rat aorta, rabbit saphenous vein, and guinea pig ileum. Thus, being a potent and selective ETB receptor antagonist, BQ-788 may be considered as a powerful tool for investigating the role of endothelins in physiological and pathological processes.

K lshikawa, M Ihora, K Noguchi, T Mose, N Wino, T Saeki, T Fukuroda, T Fukami, S Ozaki, T Nagase, et al. Biochemical and pharmacological profile of a potent and selective ETB receptor antagonist, BQ-788. Proc Noll Acad Sci USA 91:4892-4896; 1994.
T Fukuroda, T Fujikawa, S Ozaki, K lshikowa, M Yono, M NisNIdbe. Clearance of Circulating Endothelin-I by ETB Receptors in Rats. Biochemical and Biophysical Research Communications 199:1461-1465; 1994.

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