Influence of Intravesical Lower pH on the Micturition Reflex Threshold in the Rat

Aims: To investigate whether intravesical lower pH induces a micturition threshold reflex change of anaesthetized rats. Methods: Thirteen female rats, anaesthetized by α-chloralose and paralyzed by pancurone bromide were used for the experiments. The micturition threshold volume was determined by repeated cystometry. Simultaneously bladder afferent activities in four and efferent activities in seven rats were recorded from the exposed pelvic nerve to the bladder. Results: Cystometry with acidic saline at pH 3 and 4 induced a significant decrease in micturition threshold volume. The mean value of these groups of test showed that bladder compliance, micturition threshold pressure and maximal micturition contraction pressure were decreased significantly comparing with the controls. There were no changes in all other parameters recorded from afferent and efferent, e.g. afferent threshold volume, afferent or efferent activity at the micturition threshold and their peak activity at the micturition contraction. Conclusions: Acidic solution provoked sensitivity but reduced the force of the contractility to the urinary bladder. The effect was presented without a detectable change in the firing properties of bladder Aδ mechanoreceptor afferents. It is proposed that proton sensitive bladder receptors with unmyelinated afferent were stimulated by the acidic solution and that the micturition reflex was facilitated by afferent inflow from such receptors. The findings were clinically important in choosing the medium for urodynamic examination.