The effect of normal rat urine on mucosal regeneration in heterotopic urinary bladder.

A heterotopically transplanted urinary bladder (HTB) of the rat with a communicating Ommaya reservoir was developed in our laboratory as a model to elevate potential bladder carcinogens and the role of urine on the carcinogenesis. Following transplantation the mucosa undergoes ischemic necrosis, but regeneration ensues rapidly within 2 weeks. The present investigation evaluated the effect of two variants on the natural history of the HTB mucosa immediately following its transplantation: (1) presence of normal rat urine, and (2) the effect of alteration of intraluminal osmolality. The results indicate that alteration of osmolality had no effect on the regenerative process, and the epithelium returned to normal in a few weeks. Weekly administration of pooled sterile rat urine into HTB, however, induced simple hyperplasia which persisted throughout the 20-week study period. The HTBs maintained with pooled rat urine did not attain the normal ultrastructural surface characteristics even at 20 weeks posttransplantation. It is concluded that urine exerts a stimulatory effect on the bladder epithelium when first administered to HTB during the active regenerating phase and as long as urinary contact continues.