Marked reduction in percentage of rosette-forming thymocytes of rats during induction of bladder tumors and restorative effect of thymosin in vitro.

Urinary bladder carcinoma was induced in W rats by oral administration of N-butyl-N-(4-hydroxybutyl) nitrosamine [(BBN) CAS: 3817-11-6], and rosette formation of the thymus lymphocytes with Hartley strain guinea pig erythrocytes was studied until the 20th week after BBN administration. Percentage of rosette-forming cells (RFC's) began to decrease about the 8th week (stage of hypertrophy or vascular formation in the bladder wall) and remarkably declined around the 12th week (before the incidence of carcinoma) after the administration. However, no significant reduction of RFC percentage was noted in the control (without BBN) group during the observation period. Pretreatment of thymic lymphocytes from BBN-treated rats with thymosin fraction 5 (TF5), an extract from calf thymus, significantly enhanced the percentage of RFC near to that of the control level. Two (#9 and 13) subfractions separated from TF5 by high-performance liquid chromatography were found to be more effective in recovering the percentage of RFC. These results show that a maturational impairment of thymus lymphocytes may be caused from precancerous stage in BBN-administered rats and that this impairment would be restored by the thymus products in vitro.