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  • Title: Role of beta-adrenoceptor subtypes in mediating relaxation of the pig bladder trigonal muscle in vitro.
    Author: Yamanishi T, Chapple CR, Yasuda K, Yoshida K, Chess-Williams R.
    Journal: Neurourol Urodyn; 2003; 22(4):338-42. PubMed ID: 12808710.
    Abstract:
    AIMS: To investigate the role of beta-adrenoceptor subtypes in mediating relaxation of the pig bladder trigonal muscle in vitro. MATERIALS AND METHODS: Longitudinal strips of trigonal muscle were isolated, and the mucosa and serosa removed. Tissues were precontracted with KCl, and beta-adrenoceptor agonists (isoprenaline or salbutamol) were added cumulatively, and concentration-relaxation curves (CRCs) were obtained. CRCs to agonists were obtained in the absence and presence of antagonists and antagonist affinity values were calculated. RESULTS: Isoprenaline (non-selective beta-agonist) relaxed with high potency (pEC(50) = 7.2). Propranolol antagonized CRCs to isoprenaline with a high affinity (apparent pK(B) = 8.8), but the Schild plot had a slope significantly (P < 0.01) less than unity (0.61), suggesting that responses were mediated by more than one beta-adrenoceptor subtype. CGP20712A (beta(1)-antagonist) antagonized responses to isoprenaline with a low affinity (apparent pK(B) = 5.13), indicating beta(1)-adrenoceptors did not participate in the response. The affinity of ICI118551 (beta(2)-antagonist) for antagonism of responses to isoprenaline was also relatively low (apparent pK(B) = 6.9), and the Schild slopes were significantly (P < 0.01) less than unity (0.58). SR59230A (beta(3)-antagonist) antagonized CRCs to isoprenaline with a relatively low affinity (apparent pK(B) = 7.5), and with a Schild slope significantly (P < 0.01) less than unity (0.86), indicating that responses may be mediated by more than one beta-adrenoceptor subtype. In contrast to that observed with isoprenaline, the beta(2)-adrenoceptor selective agonist salbutamol induced relaxation with a relatively low potency (pEC(50) = 6.6) and with maximum responses of 80% of that to isoprenaline. ICI118551 competitively antagonized (Schild plot of unity) responses to salbutamol with a high affinity (pA2 = 8.3). CONCLUSIONS: These data suggest that beta-adrenoceptor mediated responses to isoprenaline of the bladder trigone are mediated via both the beta(2)- and beta(3)-adrenoceptor subtypes whilst responses to salbutamol appear to be mediated only via the beta(2)-adrenoceptor.
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