Pharmacological evidence for a single bradykinin B2 receptor in the guinea-pig.

1. The present study addresses the possibility of the existence of different kinin B2 receptor subtypes in the guinea-pig by evaluating the affinity of peptide and nonpeptide receptor antagonists. For this purpose, jugular vein rings, ileum segments, lung parenchymal and trachea strips were set up in organ baths for isometric tension measurements. The experiments were conducted in the presence o indomethacin (3 microM), atropine (10 microM) and captopril (10 microM). 2. BK contracted jugular vein (JV), ileum (GPI), parenchyma (LP) and trachea (GPT) with an EC50 of 13.2 +/- 1.4 nM (n=27), 11.2 +/- 2.1 (n=26), 23.6 +/- 6.3 (n=26), and 33.0 +/- 6.5 (n=27), respectively. Thiorphan, a neutral endopeptidase (EC 3.4.34.11) inhibitor and MERGETPA (DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid), a carboxypeptidase inhibitor, had no effect on the BK-induced contractions of JV, GPI and LP. In the GPT, thiorpan potentiated the contractile response to BK and was thus added in the corresponding experiments. 3. The peptide B2 receptor antagonist, Hoe 140 and the nonpeptide compound, WIN 64338, behaved as noncompetitive antagonists against contractile responses to cumulative BK in the four tissues although Hoe 140 appeared as a competitive inhibitor in the GPT only. IN order to compare the inhibitory potency of these compounds between tissues, pKB values were determined. Mean values of pKB for Hoe 140 were 8.05 +/- 0.07, 8.43 +/- 0.11, 8.13 +/- 0.18, and 8.52 +/- 0. 25 in the JV, GPI, GPT and LP, respectively. WIN 64338 gave mean pKB values of 6.89 +/- 0.10, 7.57 +/- 0.12, 7.36 +/- 0.12 adn 7.51 +/- 0.28 in the JV, GPI, LP and GPT, respectively. 4. D-Arg [Hyp3, D-Phe7, Leu8]BK and D-Arg[Hyp3, D-Phe7]BK (NPC 567) inhibited in a competitive fashion the concentration-response curves to BK. Values of pA2for each compound were not significantly different in the four tissues and were between 5.81 and 6.31 for D-Arg [Hyp3, D-Phe7, Leu8]BK and between 5.55 and 5.65 for NPC 567.