Late Radiation Damage in the Mouse Bladder as Measured by Increased Urination Frequency

Abstract

The radiation response of the mouse urinary bladder was assessed by measuring the urination frequency after localized irradiation with 1.8-MeV electrons. The onset of radiation-induced incontinence is late, no changes were observed before 5 months after doses of up to 40 Gy (4000 rad). Beyond this time good dose--response curves were obtained above a threshold dose of 15 Gy. The time of onset of radiation damage was earlier after higher doses, but in all cases the maximum damage was observed by 12 months. There was some recovery of bladder function, especially in the lower dose groups, by 16 months. The increased frequency at 5 to 12 months was associated with epithelial denudation and a loss of the specialized polyploid surface cells. Fibrosis of the deeper layers was not apparent until after 12 months. The increased urination frequency responses are correlated with the delayed compensatory proliferation of the epithelium and with the resistance of the bladder to inflation under applied pressure, which also gave a dose-response relationship at 18 months.