Cell kinetics of mouse urinary bladder epithelium. VI. Changes in the proportions of cells with various nuclear DNA content after repeated doses of propylene glycol (1,2 propanediol).

A dose of 0.2 ml propylene glycol (1,2 propanediol) was injected subcutaneously into 12 hairless mice three times a week for three months. Four animals were killed at 1, 2 and 3 months and micro-flow fluorometric histograms of the bladder epithelial cells were made. The proportion of cells in diploid S phase was not much altered, but the proportion of tetraploid S-phase cells was significantly reduced and at three months DNA synthesis in tetraploid cells completely disappeared. The proportion of diploid cells increased, the proportion of tetraploids was slightly reduced and almost all octoploid cells disappeared. The changes are qualitatively similar to those seen after the bladder carcinogen dibutylnitrosamine, and after repeated injections of cyclophosphamide, but quantitatively much less pronounced. They can be explained as a result of cell toxicity whereby propylene glycol kills some bladder epithelial cells and disturbs the mechanism of repeated DNA synthesis. Propylene glycol is thus not a completely harmless solvent and when the kinetic effects of bladder carcinogens dissolved in propylene glycol are studied, the effect of the solvent alone must be accounted for.