Abstract

The contractile responses elicited by the selective kinin B₁ and B₂ receptor agonists [desArg⁹]-bradykinin ([desArg⁹]-BK) and [Hyp³, Tyr(Me)⁸]-bradykinin ([Hyp³, Tyr(Me)⁸]-BK) (1 nM–10 μM), respectively, were evaluated in control vs. inflamed (cyclophosphamide 150 mg kg⁻¹ i.p., 48 h before the sacrifice) rat isolated urinary bladder strips. The contractile responses to the B₂ receptor agonist did not differ in control vs. inflamed bladders, whereas the contractile responses to [desArg⁹]-BK were potentiated in inflamed bladders. The selective B₁ and B₂ receptor antagonists B 9858 (H-Lys-Lys-Arg-Pro-Hyp-Gly-Igl-Ser-DIgl-Oic-OH) and Hoe 140 (H-DArg-Arg-Pro-Hyp-Gly-Thi-Ser-DTic-Oic-Arg-OH), both at 1 μM, inhibited the response to the B₁ and B₂receptor agonists, respectively, in both control and inflamed bladders. In addition, the concentration-response curve to [Hyp³, Tyr(Me)⁸]-BK was shifted to the right and depressed by B 9858 in inflamed bladders. The nonselective cyclooxygenase (COX) inhibitors S-(−)-ketoprofen (10 μM) and piroxicam (30 μM) markedly depressed the concentration-response curves to [desArg⁹]-BK and [Hyp³, Tyr(Me)⁸]-BK in control bladders, but neither drug affected the B₁ or B₂ receptor agonist-mediated responses in inflamed bladders. The selective inhibitor of the inducible COX-2 isoenzyme, NS-398 (1 μM), did not inhibit the contractile responses to [desArg⁹]-BK and [Hyp³, Tyr(Me)⁸]-BK in either control or inflamed bladders, whereas it significantly potentiated the response to the B₁ receptor agonist in inflamed bladders. The exogenous administration of prostaglandin E₂ (PGE₂) induced S-(−)-ketoprofen-resistant contractile responses that were depressed in inflamed bladders. Pretreatment with S-(−)-ketoprofen restored the PGE₂-mediated contractile responses of inflamed bladders to control values. PGE₂ assay revealed that the basal production of PGE₂ is significantly higher after inflammation than in control conditions. [desArg⁹]-BK and [Hyp³, Tyr(Me)⁸]-BK (1 μM each) both stimulated PGE₂ production, and their effect was larger in inflamed than in control bladders. Piroxicam (30 μM) prevented the PGE₂ production evoked by [desArg⁹]-BK in both control and inflamed bladders and likewise abolished that produced by [Hyp³, Tyr(Me)⁸]-BK. NS-398 (1 μM) reduced the PGE₂ production elicited by [desArg⁹]-BK in control and inflamed bladders. When NS-398 was tested on the [Hyp³, Tyr(Me)⁸]-BK-induced PGE₂ production, it inhibited PGE₂ production in the inflamed bladders only, without significantly modifying the response obtained in controls. These findings demonstrate that 1) in normal bladders, the activation of B₁ and B₂ receptors evokes contraction that is largely mediated by COX-1 metabolites, whereas the COX-2 appears to be involved in PGE₂ production after the activation of B₁ receptor only, without interfering with contraction, and 2) in inflamed bladders, the activation of B₁ and B₂ receptors still produce PGE₂, but the contractile response is not reduced by COX inhibitors, a result that indicates that additional mechanisms play a compensatory role.