Association of cyclophosphamide-induced male-mediated, foetal abnormalities with reduced paternal germ-cell apoptosis.

To investigate the mechanism by which malformed offspring can result from the exposure of males to mutagens, we treated adult male rats with 0, 1.4, 3.4 or 5.1 mg/kg cyclophosphamide, 6 days per week for 9 weeks, a treatment regimen known to induce heritable abnormalities. Testis samples from some of the animals were then collected for fixation in Carnoy's fluid and subsequent analysis of germ-cell apoptosis and proliferation. The remainder were mated, resulting in a greater than 11-fold increase in the proportion of abnormal offspring produced in the 5.1 mg/kg group. The number of apoptotic cells per stage XII/XIII tubular cross-section decreased with increasing dose, significantly so at 5.1 mg/kg (P<0.05). No statistically significant effect was found on spermatocyte numbers at this dose, indicating that a reduction in the amount of cells available to undergo apoptosis cannot explain the decrease. The inappropriate survival of damaged germ-cells caused by a lowering of the incidence of apoptosis may, therefore, account for the rise in the proportion of foetal malformations.