Effects of intravesical instillation of antimuscarinics on bladder overactivity induced by intravesical instillation of adenosine triphosphate in rats

Abstract

Purpose Adenosine triphosphate (ATP) from the urothelium acts as a sensory neurotransmitter and is augmented in many diseases, such as overactive bladder. We investigated the effects of intravesical instillation of oxybutynin on ATP-induced bladder overactivity to determine whether this effect is mediated by effects on urothelial muscarinic receptors.

Materials and Methods Cystometry (at rate of 0.04 ml/min) was performed in female Sprague-Dawley rats (body weight 250 g) under urethane anesthesia (1.2 g/kg). After a 2-hour baseline period, protamine sulfate (10 mg/ml) was instilled for 1 hour, and then ATP (60 mM, pH 6.0) or a mixture of oxybutynin (10-6 M) and ATP (60 mM, pH 6.0) was instilled intravesically. We performed experiments with 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP) and methoctramine by the same methods. Cystometric parameters, such as the intercontraction interval (ICI), pressure threshold (PT), and maximal voiding pressure (MVP), were compared.

Results With intravesical instillation of ATP after protamine sulfate treatment, the ICI was decreased compared with baseline (ICI: baseline, 487.1±64.8 s; protamine, 450.6±56.1 s; ATP, 229.7±35.3 s; p<0.05). Addition of oxybutynin, 4-DAMP, or methoctramine in the ATP solution did not significantly change the ICI compared with ATP solution alone (ICI: oxybutynin, 189.1±32.3 s; 4-DAMP, 161.1±22.8 s; methoctramine, 341.0±113.3 s; p>0.05). Intravesical instillation of ATP decreased MVP and PT significantly compared with baseline, but MVP and PT were not changed significantly with oxybutynin, 4-DAMP, or methoctramine compared with ATP.

Conclusions Bladder overactivity induced by intravesical instillation of ATP was not suppressed by intravesical instillation of antimuscarinics. Suppression of ATP-induced bladder overactivity by intravenous oxybutynin is not mediated by urothelial muscarinic receptors.