Effects of Tritium-Labeled Pyrimidine Nucleosides on Epithelial Cell Proliferation in the Mouse: I. Cytodynamic Perturbations in Normal Circadian Rhythms after a Single Injection of 3 H-Thymidine

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Abstract
In a combined stathmokinetic, autoradiographic and microspectrophotometric study on the cytodynamics in mouse epidermis, circardian rhythms were observed in number of cells within the various phases (except G2) of the mitotic cell cycle, and in mitotic rate. S-Phase influx and efflux varied during a 24 h period. No diurnal rhythm was observed in mitotic rate in the epithelium of small intestine. 3H-Thymidine [3H-TdR] (1 .mu.Ci/g; sp act [specific activity] 5 Ci/mmol) induced mitotic delay in labeled cells 2-8 h after administration. A supranormal mitotic activity in unlabeled cells was observed 12-24 h after injection of 3H-TdR. Unlabeled thymidine had no effects on epidermal cell proliferation.. S-Phase duration and average cell cycle time were estimated by traditional cell kinetic methods. A 3H-TdR-induced synchrony in cells entering the S phase 0-15 h may occur after injection of the precursor. A mitotic delay was seen in small intestinal epithelium 2-6 h after injection of the precursor.