Hoe 140 a new potent and long acting bradykinin‐antagonist: in vitro studies

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Abstract
Hoe 140 (d‐Arg‐[Hyp3, Thi5, d‐Tic7, Oic8]bradykinin) is a new bradykinin (BK)‐antagonist. It was tested in several in vitro assays and compared with d‐Arg‐[Hyp2, Thi5,8,d‐Phe7]BK. In receptor binding studies in guinea‐pig ileum preparations, Hoe 140 showed an IC50 of 1.07 × 10−9mol l−1 and a KI value of 7.98 × 10−10 mol l−1. In isolated organ preparations Hoe 140 and d‐Arg‐[Hyp2, Thi5,8, d‐Phe7]BK inhibited bradykinin‐induced contractions concentration dependently, with IC50‐values in the guinea‐pig ileum preparation of 1.1 × 10−8 mol l−1 and 3 × 10−5 mol l−1, respectively. pA2 values in this tissue were 8.42 and 6.18, respectively. In the rat uterus preparation the IC50 value was 4.9 × 10−9 mol l−1 for Hoe 140. d‐Arg‐[Hyp2, Thi5,8, d‐Phe7]BK showed an IC50 of 4.0 × 10−6 mol l−1. The IC50 values in the guinea‐pig isolated pulmonary artery were 5.4 × 10−9 mol l−1 and 6.4 × 10−6 mol l−1, respectively. In the rabbit aorta no inhibitory effects on Des‐Arg9‐BK induced contractions were observed. In cultured bovine endothelial cells, Hoe 140 antagonized (IC50 = 10−8 mol l−1) bradykinin‐induced endothelium‐derived relaxing factor (EDRF) release and the bradykinin‐induced increase in cytosolic free calcium (IC50 = 10−9 mol l−1). Hoe 140 (10−7 mol l−1) totally suppressed the bradykinin‐induced (10−8 to 10−4mol l−1) prostacyclin (PGI2) release from cultured endothelial cells of bovine aorta. d‐Arg‐[Hyp2, Thi5,8, d‐Phe7]BK (10−7 mol l−1) showed a weaker antagonism. Taken together these results show that Hoe 140 is a highly potent bradykinin antagonist. It was two to three orders of magnitude more potent than d‐Arg‐[Hyp2, Thi5,8, d‐Phe7]BK.