| Abstract: | The circulating leukocyte is usually considered a mature, differentiated cell which does not normally divide. Cytophotometry of human and mouse leukocyte nuclei, however, reveals significant fluctuations in amounts of Feulgen-DNA in all leukocytes at various times of the day. When analyzed for DNA content by the diphenylamine method, the same samples demonstrate variations closely correlated with those obtained by cytophotometry. Although these data may be interpreted as suggesting, among other things, the presence of metabolic DNA, a preliminary radioautographic study of the uptake of tritiated thymidine in mouse leukocytes failed to demonstrate evidence of DNA synthesis in the entire population of cells. In this study only 6–7% of the total leukocyte population was labelled over a 24-hour period. This discrepancy, when considered in light of other uncertainties concerning the Feulgen and diphenylamine reactions, has led to reservations over the ability of either reaction to reflect the true amount of DNA in cells at all times. Rather, we consider it more likely that both procedures reveal similar incomplete fractions of leukocyte DNA at various times of the day, and that the magnitude of this fraction is, perhaps, determined by cyclic influences acting on such parameters as nuclear volume and degree of packing of the nucleohistones. |
