Mechanisms of reactivity of urinary bladder smooth muscle

Mechanism of bladder smooth muscle contraction and relaxation and its pharmacological influence in various pathologic states are of incremental interest of investigators and clinicians.

The aim of our study was to assess the reactivity of urinary bladder smooth muscle in guinea pigs to two different pharmacological agents.

We compared the in vitro reactivity of smooth muscle strips of guinea pig urinary bladder to muscarinic stimulation by carbachol and acetylcholine. We prepared two kinds of strips, urothelium-denuded and with intact urothelium. Both kinds of strips were aerated under tension in Krebs-Henseleit's solution in organ-bath for 1 hour and after that cumulative concentration-response curves to carbachol (10(-9) - 10(-5) mol/l) and acetylcholine (10(-8) - 10(-3) mol/l) were constructed.

We observed significantly higher reactivity of smooth muscle strips to carbachol, comparing to acetylcholine at the same concentrations both in strips with urothelium (at concentration 10(-5) mol/l: 22.1 g/100 mg vs 6.1 g/100 mg) and in urothelium-denuded strips (at concentration 10(-5) mol/l: 24.5 g/100 mg vs 5.1 g/100 mg). The reactivity differences between strips with and without urothelium were not significant, however, in higher concentrations of acetylcholine (10(-4) and 10(-5) mol/l) and carbachol (10(-6) and 10(-5) mol/l) we noticed no significant inhibition of contractile response of smooth muscle strips with intact urothelium.

In our experiments we confirmed that carbachol was more potent constrictor than acetylcholine in detrusor smooth muscle strips of guinea pigs. The presence of urothelium did not change the reactivity significantly. (Fig. 4, Ref: 23.).