Some cell kinetic effects of combined injury with ionizing radiation and cyclophosphamide on mouse bladder urothelium.

Cyclophosphamide was given intraperitoneally to groups of eight female mice 48 h after local electron irradiation to the bladder with 0, 10 and 20 Gy respectively. The reactions in the urothelium were monitored by histology, incorporation of tritiated thymidine and flow cytometry. A wave of increased thymidine incorporation combined with an increase in the proportion of diploid S-phase cells was seen in the unirradiated bladders 24 h after the drug treatment, followed by normalization after 1 week. This response was significantly less pronounced in the irradiated animals. In the unirradiated animals a similar wave characterized by an increased proportion of octaploid cells was also seen, but this wave occurred later in the irradiated animals. Severe injury was observed in the rectum of the 20 Gy-irradiated animals. Irradiation prior to drug treatment led to only small effects, but a decreased ability for regenerative DNA synthesis after drug injury seems to persist. This affects both proliferation and the building up of polyploidy.