A study of antitumor effects of thymosin on rat and mouse urinary bladder carcinoma induced by N-butyl-N-(4-hydroxybutyl)-nitrosamine.

N-Butyl-N-(4-hydroxybutyl)-nitrosamine (BBN), which induces bladder carcinoma in female Wistar rats and female C3H/HeJ mice, was given as 0.025% (w/v) solution to rats and 0.05% to mice in the drinking water. Thymosin fraction 5 (TF5) or thymosin alpha 1 (T alpha 1) dissolved in normal saline, and normal saline (control) respectively were injected into the right thigh IM twice a week in the experimental rats. At the 30th week of BBN oral administration, weights of urinary bladder were different among the three groups. Bladder weights and incidence of bladder carcinoma were significantly lower in the TF5-treated group as compared with control group. Natural killer cell activity of splenic lymphoid cells was significantly elevated in the TF5-treated group as compared with the control group. However, these parameters were not significantly different between the T alpha 1-treated group and control saline-treated group. On the other hand, bladder weights and incidence of bladder carcinoma were not significantly different among TF5-, T alpha 1- and saline-treated groups at 10, 15, 20, and 25 weeks of BBN administration in mice according to the same protocol as rats.