Thymidine-3H, 125μc, was injected intravenously into each of 11 male rats. The rats were killed one hour after injection, at four-hour intervals during a 24-hour period. Epithelial specimens were separated from the underlying connective tissue and subjected to liquid scintillation. The results indicated that maximal DNA synthesis occurred at 4:30 to 8:45 AM and that minimal synthesis occurred at 3:40 to 8:30 PM.
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