Induction of urinary bladder hyperplasia in Sprague-Dawley rats orally administered tri-n-butyl phosphate

The effects of tri-n-butyl phosphate (TBP) were investigated in the Sprague-Dawley rat over an 18-wk period. Groups of randomized female (average weight [AW] = 206 +/- 10 g) and male (AW = 294 +/- 13 g) rats were divided into low-dose, high-dose, and control groups (12 rats/sex X group). Tri-n-butyl phosphate was administered by gavage once a day for 5 days/wk over an 18-wk period. Low-dose animals received 0.20 g/kg X day throughout the experiment and high-dose animals received 0.30 g/kg X day for the first 6 wk. For the remaining 12 wk, the high-dose level was increased to 0.35 g/kg X day. Histopathological examination of tissues revealed that all test rats examined developed diffuse hyperplasia of the urinary bladder epithelium. Similar changes were not found in the control animals.