FR 173657: a new, potent, nonpeptide kinin B2 receptor antagonist. An in vitro study

FR 173657, the first effective nonpeptide kinin B2 receptor antagonist, has been tested in four preparations from different species (human, pig, rabbit, and guinea pig). The new compound shows high apparent affinity for the four B2 receptors, with pA2 values ranging from 8.2 to 9.4 FR 173657 is a selective B2 receptor antagonist that does not interact with human, pig, or rabbit B1 receptors. The new compound is extremely specific for the kinin B2 receptors as it does not affect the myotropic effects of norepinephrine, endothelin-1, or 5-hydroxytryptamine in the human umbilical vein; the contractions elicited by substance P and angiotensin II in the rabbit jugular vein or those produced by acetylcholine and histamine in the guinea pig ileum; or the relaxation of the pig coronary artery induced by norepinephrine and substance P. FR 173657 acts as a competitive antagonist over an extended range of concentrations on human and rabbit B2 receptors, whereas on pig and guinea pig receptors, it depresses the maximal effect of bradykinin and thus appears to act as a noncompetitive antagonist.