Role of ?-adrenoceptor subtypes in mediating relaxation of the pig bladder trigonal muscle in vitro

Aims To investigate the role of β-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 β-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 β-agonist) relaxed with high potency (pEC50 = 7.2). Propranolol antagonized CRCs to isoprenaline with a high affinity (apparent pKB = 8.8), but the Schild plot had a slope significantly (P