The effects of β-adrenoceptor agonists on KCl-induced rhythmic contraction in the ureter of guinea pig

Abstract

In the present study, we tried to determine what effects were induced by β-adrenoceptor agonists on 40 mM KCl-induced rhythmic contraction and to clarify which β-adrenoceptor subtypes are involved in the regulation of ureter motility in the guinea pig by using in vitro functional analysis. 40 mM KCl-induced rhythmic contraction was abolished by papaverine (10-6 M), nicardipine (10-5 M) and cromakalim (10-5 M), but was not influenced by atropine (10-6 M). Isoprenaline decreased the amplitude, and changed the pattern of 40 mM KCl-induced rhythmic contraction in concentration-dependent manner. These results suggest the possibility that the stimulation of β- adrenoceptors may regulate the ureteral peristalsis. Salbutamol (selective β2-AR agonist) and CGP12177 (β(1,2)-AR antagonist and β3-AR partial agonist) were also effective in decreasing the amplitude and changing the pattern of the rhythmic contraction. The pD2 values of agonists were 7.57 (isoprenaline), 5.80 (CGP12177) and 7.63 (salbutamol), respectively. The concentration-response curves of isoprenaline and salbutamol were rightward shifted by the presence of propranolol, and the apparent pA2 values for propranolol against isoprenaline and salbutamol were 7.12 and 6.29, respectively. These results suggest that inhibition for 40 mM KCl-induced rhythmic contraction of the ureter by isoprenaline and salbutamol mediated mainly via atypical β-adrenoceptor subtype.