[Denervation supersensitivity of the detrusor muscle due to prolonged bladder overdistension]

The influence of prolonged bladder overdistension on the detrusor muscle was studied in female mongrel dogs. Two overdistending methods were employed, namely, constantly elevated hydrostatic pressure for one hour and bladder neck ligation for 48 hours. The cystometrogram and urinalysis at 2 weeks after release of overdistension were compared with the preoperative estimations. Using the in vitro isometric technique, the contractility of the detrusor muscle strip to acetylcholine was evaluated in the untreated control group and the two overdistended groups. Prolonged bladder overdistension for one hour as well as 48 hours resulted in a high incidence of urinary tract infection. There was no correlation between the cystometric findings before and after overdistension . An increase in contraction response to acetylcholine was observed in both overdistended groups. Besides, a small contraction response to acetylcholine at a lower concentration was observed in the group overdistended for 48 hours. It is suggested that the observed contraction response increase was probably due to axonal degeneration caused by a decrease in the blood supply to the overdistended bladder wall.