Classification of kinin receptors.

This minireview is divided into three parts: the first part refers to the characterization and classification of kinin receptors using agonists and antagonists in isolated tissues (classical pharmacology). Two kinin receptors have been considered on the basis of their distinct pharmacology, namely the B1 receptor of the rabbit aorta (rank order of potency of agonists: LysdesArg9BK > desArg9BK > or = LysBK > BK; apparent affinities of antagonists Lys[Leu8]desArg9BK (pIC50 8.4) > [Leu8]desArg9BK (pIC50 7.4) >>> HOE 140, a B2 receptor antagonist, pIC50<5.0), and the B2 receptor of the rabbit jugular vein (potency of agonists: LysBK = BK >>> LysdesArg9BK = desArg9BK and HOE 140 (pIC50 9.0) >>> Lys[Leu8]desArg9BK, pIC50<5.0). The second part describes species-related B1 receptor subtypes, demonstrated by different pharmacological profiles of agonists and antagonists: human, rabbit and pig subtypes (LysdesArg9BK >> desArg9BK and Lys[Leu8]desArg9BK > [Leu8]desArg9BK) and dog, rat, mouse and hamster B1 receptors (desArg9BK = LysdesArg9BK and [Leus]desArg9BK = Lys[Leu8]desArg9BK). Affinities of agonists and antagonists in some species (man, rabbit, pig) are significantly increased (at least 10-fold) by the presence of a Lys at their N-terminus. The last part describes species-related B2 receptor subtypes supported by results obtained with non-peptide receptor agonists (FR 190997) and antagonists (FR 173657). While BK acts as a full agonist in man, rabbit and pig, FR 190997 behaves as a full agonist on human, as partial agonist on rabbit, and as pure antagonist on pig B2 receptors. Various hypotheses are considered to interpret these findings.

Kinin B1 receptor antagonists containing alpha-methyl-L-phenylalanine: in vitro and in vivo antagonistic activities.

-To protect from metabolism and to improve potency of the AcLys-[D-betaNal7,Ile8]desArg9-bradykinin (BK) (R 715), we prepared and tested 3 analogues containing alpha-methyl-L-Phe ([alphaMe]Phe) in position 5: these are the AcLys-[(alphaMe)Phe5,D-betaNal7, Ile8]desArg9BK (R 892), Lys-Lys-[(alphaMe)Phe5,D-betaNal7, Ile8]desArg9BK (R 913), and AcLys-Lys-[(alphaMe)Phe5,D-betaNal7, Ile8]desArg9BK (R 914). The new compounds were tested against the contractile effect induced by desArg9BK on 2 B1 receptor bioassays, the human umbilical vein, and the rabbit aorta. Their antagonistic activities were compared with those of the early prototypes (Lys-[Leu8]desArg9BK and [Leu8]desArg9BK) and with other recently described peptide antagonists. The 3 (alphaMe)Phe analogues showed high antagonistic potencies (pA2) at both the human (8.8, 7.7, and 8. 7, respectively) and rabbit (8.6, 7.8, and 8.6, respectively) B1 receptors. No antagonistic effects (pA2<5) were observed on the B2 receptors that mediate the contractile effects of BK on the human umbilical vein, the rabbit jugular vein, and the guinea pig ileum. Moreover, these new B1 antagonists were found to be resistant to in vitro degradation by purified angiotensin-converting enzyme from rabbit lung. The Nalpha-acetylated forms, R 892 and R 914, were resistant to aminopeptidases from human plasma. In vivo antagonistic potencies (ID50) of B1 receptor antagonists were evaluated in anesthetized lipopolysaccharide-treated (for B1 receptor) and nontreated (for B2 receptor) rabbits against the hypotensive effects of exogenous desArg9BK and BK. R 892 efficiently inhibited (ID50 2.8 nmol/kg IV) hypotension induced by desArg9BK without affecting that evoked by BK (ID50 >600 nmol/kg IV). Conversely, the peptide antagonists Lys-Lys-[Hyp3,Igl5,D-Igl7,Oic8]desArg9BK (B 9858) and DArg-[Hyp3,Thi5,D-Tic7,Oic8] desArg9BK (S 0765) showed dual B1/B2 receptor antagonism in vitro and in vivo. It is concluded that R 892 and congeners provide selective, highly potent, and metabolically stable B1 kinin receptor antagonists that can be useful for the assessment of the physiological and pathological roles of kinin B1 receptors.

Effects of kinins on isolated stomachs of control and transgenic knockout B2 receptor mice.

The aim of this study was to investigate the pharmacological profile of the kinin B1 and B2 receptors in isolated stomachs from wild-type control and B2 receptor knockout mice. Isometric contractions evoked by bradykinin (BK) (9 nM) and desArg9BK (28 nM) were shown to be different. The contraction induced by desArg9BK had a longer duration than that evoked by BK and increased during incubation in vitro in stomachs of wild-type controls, while in the transgenic B2 receptor knockout mice, the contractions evoked by desArg9BK and BK were similar and followed the B1 receptor agonist pattern. BK but not the carboxypeptidase-resistant analog, [Phe8psi(CH2-NH)Arg9]BK, was found to be active in the stomach of B2 receptor knockout mice. BK-induced contractions were prevented by mergetpa (a carboxypeptidase M inhibitor) (10 microM) and by a the B receptor antagonist, AcLys[DbetaNal7,Ile8]desArg9BK (R 715) (0.88 microM), while not being influenced by the B2 receptor antagonist HOE 140 (0.38 microM). BK and [Phe8psi(CH2-NH)Arg9]BK were potent contractants of the wild-type mice stomach and their effects were not influenced by mergetpa or by the B receptor antagonist: they were reduced by HOE 140. After incubation in vitro for 3-4 hours, the tissues were treated with HOE 140 (4 microM) and FR-173657 (17 microM) to eliminate B2 receptor function. In these tissues, BK evoked a B1-like contraction which was inhibited by mergetpa (10 microM) and antagonized by R 715 (8 microM). The results indicate that BK acts primarily on B2 receptors. However, after intramural conversion to desArg9BK, activation of B1 receptors of the mice stomach occurs. In the tissues of B2 receptor knockout mice, BK behaves as a pure B1 receptor agonist while in stomachs of control animals, the B2 receptor contribution is overwhelming. After complete blockade of the B2 receptor, BK is able to evoke B1-mediated responses similar to those observed in tissues of B2 receptor knockout mice. It is concluded that the disruption of the B2 receptor gene eliminates the B2 receptor without influencing the B1 receptor system.