Kinin B1 and B2 receptors in pig vessels: characterization of two monoreceptor systems

The coronary artery and renal vein of the adult pig are sensitive and reliable monoreceptor systems for studying kinin receptors. The pig coronary artery with intact endothelium is highly sensitive to bradykinin (BK, pEC50 8.6), while being insensitive to the B1 receptor agonist, LysdesArg9BK. The tissue responds to BK with concentration-dependent relaxation, which is prevented by B2 receptor antagonists, particularly DArg[Hyp3, Thi5, DTic7, Oic8]BK (HOE 140, pKB 9.3), (E)-3-(6-acetoamido-3-pyridyl)-N-(N-{2, 4-dichloro-3-[(2-methyl-8-quinolinyl)oxy-methyl]phenyl}-N- methylaminocarbonyl-methyl)acrylamide (FR 173657), a new non peptide compound (pKB 9.3), while B1 receptor antagonists (e.g. Lys[Leu8]desArg9BK) are inactive. The order of potency of kinin-related peptides in this vessel is: LysBK > or = BK > [Hyp3]BK > [Aib7]BK, a sequence typical of a B2 receptor system. Antagonists such as HOE 140 and FR 173657, at high concentrations reduce the maximum effect of BK and thus behave as noncompetitive antagonists. The kinin B1 receptor was studied in the pig renal vein without endothelium and incubated for several hours in order to allow for the de novo formation of this functional site. After 7-8 h in vitro incubation, the vessel shows high sensitivity to LysdesArg9BK (pEC50 8.3) and is insensitive to BK. The pig renal vein responds to B1 receptor agonists with concentration-dependent contraction which maintains a stable plateau and is prevented by selective B1 receptor antagonists such as Lys[Leu8]desArg9BK (pKB 6.7). The most active antagonist has been found to be desArg9HOE 140 (pA2 7.6) which acts as competitive antagonist in this preparation. Some B2 antagonists (e.g. HOE 140) show weak (pKB 6.1) anti-B1 receptor activity while the non-peptide compound FR 173657 is inactive on the B1 receptor and therefore acts as a potent and selective kinin B2 receptor antagonist in the pig. The data obtained in this study allow us to compare the porcine B2 and B1 receptors with those of other species including man, and underline some interesting features that are unique to the porcine functional sites.