Diurnal Variation of Proliferative Activity in the Human Bone Marrow

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Abstract
A study was made of the possible diurnal variation of proliferative activity of human bone marrow cells. A distinct diurnal variation of mitotic indices was present in 5 of 6 normal subjects. The average number of mitotic figures per 1000 nucleated cells in the 6 subjects was 7.6 at 6:00 a.m., 9.5 at noon, 10.5 at 6:00 p.m., and 13.1 at midnight. An assessment of diurnal variation in the per cent of cells synthesizing deoxyribonucleic acid was made in 4 additional subjects by means of incubation of aspirated marrow samples with tritiated thymidine in vitro. By this method, no consistent variation of synthesis could be found in erythroid precursor cells, but the per cent of myeloid precursor cells incorporating the label was lowest at midnight in each subject.

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