Cell kinetics of mouse urinary bladder epithelium. IV. Changes in cell proliferation, nuclear DNA content, and number of diploid, tetraploid and octoploid cells after a single dose of dibutylnitrosamine.

The initial effect of a single subcutaneous injection of 0.01 ml of dibutylnitrosamine on the mouse (hr/hr strain) urinary bladder epithelium was a block in DNA synthesis in the diploid cells followed by a regenerative reaction. This did not, however, lead to a subsequent wave of increased DNA synthesis among the tetraploid cells. Later, a new wave of DNA synthesis occurred among the diploid cells, and again there was no subsequent wave of tetraploid DNA synthesis. The total cell number was not affected. These disturbances resulted in periods of reduced numbers of octoploid cells. This effect was unlike that obtained in previously published experiments using cyclophosphamide, which led to considerable hyperplasia, especially of octoploid cells, and no disturbance of tetraploid DNA synthesis. Thus the action of a single dose of dibutylnitrosamine on the epithelial cells in the mouse urinary bladder is very different from that of cyclophosphamide in a single dose, but it is not possible to say whether this has anything to do with the carcinogenicity of the nitrosamine.