Beta-adrenoceptors in the detrusor of guinea pig bladder

In the present study, we tried to determine which beta-adrenoceptor subtypes are involved in the inhibitory regulation of bladder motility in the guinea pig by using in vitro functional analysis. Isoprenaline, norepinephrine and epinephrine decreased spontaneous contractile activity of the bladder concentration-dependently, the rank order of their potency being isoprenaline (pD2 = 7.38)>norepinephrine (6.71)>epinephrine (6.31). Dobutamine was also effective in inhibiting the spontaneous contraction (5.81). However, CGP-12177, BRL37344, salbutamol, and clenbuterol were not effective at the concentration of 30 microM. The concentration response curves of catecholamines (isoprenaline, norepinephrine and epinephrine) were rightward shifted by the presence of atenolol. Schild regression analyses carried out for atenolol against isoprenaline, norepinephrine and epinephrine gave pA2 values of 6.93, 6.78 and 6.69, respectively. The concentration-response curve for isoprenaline was unaffected by 10 microM butoxamine. In the presence of 1 microM propranolol, bupranolol produced shifts of the concentration-response curve for isoprenaline, and the apparent pA2 value for bupranolol against isoprenaline was 5.50. These results suggest that the inhibition of spontaneous contraction of the guinea pig bladder by beta-adrenoceptor agonists is mediated mainly via beta1-adrenoceptor and the effect of isoprenaline is mediated partly via atypical beta-adrenoceptor subtype.