The contribution of sensory nerves to xylene-induced cystitis in rats.

The role of capsaicin-sensitive sensory nerves of the rat urinary bladder in xylene-induced cystitis was investigated. Instillation of xylene into the urinary bladder of female rats induced cystitis, e.g. detrusor hyperreflexia and increased vascular permeability. Detrusor hyperreflexia was also observed in rats desensitized to capsaicin as adults (50-125 mg/kg s.c., 4 days before) but only for a short period (1 h) after instillation. When a longer time lag (24 h) was allowed to elapse following instillation, reflex micturition was almost abolished. In rats desensitized to capsaicin as newborns (50 mg/kg s.c. on second day of life) reflex micturition was almost abolished and xylene (given 1 h before measurement) was ineffective. The xylene-induced plasma extravasation was greater in the bladder neck than in the dome. In the bladder neck the "early" response to xylene was reduced but not abolished in rats densensitized to capsaicin as adults or pretreated with compound 48/80 and was abolished in rats desensitized to capsaicin as newborns. The bladder content of substance P-like immunoreactivity decreased at various times following xylene instillation but this change occurred in parallel to the increase in bladder weight. These findings indicate that xylene-induced cystitis involves, at least in part, an irritation of capsaicin-sensitive sensory nerves in the bladder wall. The present results further suggest that xylene acts by stimulating at least two populations of sensory nerves which differ in their sensitivity towards capsaicin.