Diurnal Variation of Proliferative Activity in the Human Bone Marrow.

S APPROPRIATE cell labels have become available in recent years, much information concerning the rate of cell growth in the bone marrow has been obtained. Basic to many of the studies have been the assumptions that the proliferating cells under observation are uniform as to proliferative potentials and undergo cell division in a purely random manner. The mitotic activity of some mammalian proliferating cell systems, however, has been shown to vary with a regular diurnal rhythm.’ #{176} If significant diurnal variation in the rate of cell division occurred in the human marrow, some change in the approach to calculations of cell growth rates would have to be made. This factor would be particularly important if measurements of mitotic indices or the per cent of cells synthesizing deoxyribonucleic acid as determined by incorporation of labeled precursor substances were used in assessing proliferative activity of the cell population. The purpose of the study reported here, therefore, was to determine if significant diurnal variation in proliferative activity of human bone marrow cells could be demonstrated. The two measures of proliferative activity that were used for study were the mitotic index determined by the method of J apa and an assessment of the per cent of cells in DNA synthesis by in vitro incubation of marrow samples with tritiated thymidine.