Elimination of cyclophosphamide-induced SCE in lymphocytes of rats with time post-treatment.

Rats were treated intraperitoneally (ip) with 13.3 mg cyclophosphamide (CP)/kg. Blood was obtained by cardiac puncture 6,24,48,72 hr, 5 da and after treatment. The spontaneous sister chromatid exchange (SCE) frequency (9.94 SCEs/cell) was 4-fold increased (40.49 SCE/cell) in lymphocyte cultures set up 24 hr, after the CP treatment. Within the next 24 hr the SCE frequency began to decline and by 2 wk post-treatment the SCE values were within the control range. The results indicate that the elimination of damage to DNA by existing repair mechanisms is responsible for the reduction of SCEs with time, in addition to lymphocyte turnover.