Circadian rhythms in phases of the cell cycle in the hamster as demonstrated by flow cytometry.

Abstract

Circadian rhythmicity in the phases of the cell cycle of several epithelial tissues of the hamster was analysed by flow cytometry. Hamsters were killed every 3 hr for 24 hr to permit observation of the effect of 'time of day' on the proportion of cells in the various phases of the cell cycle. Bone marrow and epithelium from cheek pouch, oesophagus and tongue were isolated and processed to single cell suspensions for analysis. The only systematic difference in the collection of the data was the time of day when the hamsters were killed. From the resulting DNA histograms, derived by flow cytometry (which was chosen as the technique for this study because of demonstrated applicability in determining cellular properties), the G1, S, and G2 fractions were estimated. Multiple linear regression techniques were used to estimate circadian periodicity in the data. The calculated circadian rhythms in tongue and oesophagus, derived by flow cytometry, were consistent with murine rhythms previously reported, as derived by other techniques. Circadian rhythms also were demonstrated by flow cytometry to be present in the cheek pouch epithelium, as has been reported by others. Although there was considerable fluctuation in findings from the bone marrow, the fluctuation was not of circadian periodicity, perhaps because of the mixed cell population. This study validates the reliability of older techniques, such as mitotic indices, labelling indices, and uptake of tritiated thymidine, which show the rhythmic nature of cell division in vivo.