Pharmacological and molecular evidence for kinin B₁ receptor expression in urinary bladder of cyclophosphamide‐treated rats

Abstract

1. In the present study, we developed an experimental model of cystitis induced by cyclophosphamide (CYP). In order to characterize des-Arg9-BK-induced contraction on the urinary bladder (UB) during the development of inflammation and to quantify kinin B1 receptor gene expression using a quantitative RT - PCR technique. 2. In the presence of peptidase inhibitors captopril (10 microM), DL-thiorphan (1 microM) and DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid (MERGEPTA 5 microM), bradykinin (BK) (0.3 - 3,000 nM) evoked a concentration-dependent contraction of rat UB which was not different between the CYP- and vehicle-treated groups. Unlike BK, des-Arg9-BK (0.3 - 100,000 nM) did not contract UB from vehicle-treated rats but contracted vigorously bladder strips from CYP-treated rats 14, 24 and 168 h after treatment. In UB of 24 h treated rat, the pD2 value of des-Arg9-BK was 7.3+/-0.1. 3. The cyclo-oxygenase inhibitor indomethacin (3 microM) reduced by 30% the maximal response of des-Arg9-BK. Both the kinin B1 receptor antagonists des-Arg9-[Leu8]BK (10 microM) and des-Arg10-Hoe 140 (10 microM) produced a rightward shift of the concentration-response curve to des-Arg9-BK yielding pKB values of 6.8+/-0.2 and 7.2+/-0.1, respectively, whilst the kinin B2 receptor antagonist Hoe 140 (1 microM) had no effect. 4. After CYP treatment, mRNA coding for the kinin B1 receptor appeared predominantly in UB. In this organ, the induction was progressive, reaching a maximum 48 h after CYP treatment. 5. In conclusion, the present study provides strong evidence for an induction of kinin B1 receptors in UB of CYP-treated rats. This was associated at a molecular level with an increase in mRNA expression of the gene coding for the kinin B1 receptor. This kinin receptor displayed the whole features of a classical rat kinin B1 receptor.