Diurnal variation of DNA synthesis in premalignant hamster cheek pouch.

The right cheek pouch of hamsters was painted twice a week with DMBA for 4 and 7 weeks in different groups. It was found that there were diurnal rhythms and non-random distributions of DNA synthesis and mitotic events in DMBA-treated hamster-cheek-pouch epithelium. The degree of these changes was markedly greater than the changes in non-treated control pouches. The finding of cluster formation was described as 'symphokinesis', the non-random grouping of basal cells with synchronous DNA cycles during tissue growth.