Transient and persistent hyperplasia in heterotopically transplanted rat urinary bladders induced by formalin and foreign bodies.

The effects of formalin instillation or teflon bead insertion on heterotopically transplanted rat urinary bladders (HTBs) were investigated. A single instillation of 0.3 per cent formalin dissolved in 0.9 per cent NaCl into HTBs induced multifocal superficial ulcers which were quickly repaired by lateral spreading of regenerating cells migrating from the adjacent mucosa. This was associated with a sharp increase in labeling index (10-30 per cent) on days 1 and 2, followed by focal mild (up to five cell layers) simple hyperplasia (SH) on days 4 and 7. Repeated weekly instillation of formalin for 30 weeks induced only focal mild epithelial hyperplasia. Six weekly instillations of urine one day after formalin administration slightly enhanced the formalin-induced rise in labeling index. Insertion of teflon beads caused extensive diffuse remarkable changes, especially in the presence of urine: multifocal to diffuse SH (four to eight cell layers) and multifocal papillary or nodular hyperplasia was observed by six weeks. The results indicate that responses to formalin instillation are acute and transient, while reactions to bead insertion are persistent. In both cases, presence of urine appeared to enhance hyperplastic changes. These models of bladder injury, by inducing two different types of reactions in the bladder, may be useful in examining the role of trauma in bladder carcinogenesis.