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CIRCADIAN INFLUENCE ON THE WAVE FORM OF THE FREQUENCY OF LABELED MITOSES IN MOUSE CORNEAL EPITHELIUM

The FLM was studied in mouse corneal epithelium at two different phases of the mouse circadian system. The following results were obtained: (1) a circadian rhythm was found in the corneal mitotic index of both experimental groups, with the peak near 09.00 hours, the trough near 21.00 hours and a 10‐fold difference in values between the peak and the trough; (2) when 3H‐TdR was injected at 09.00 hours, the first wave of labelled mitoses rose earlier, attained a broader peak and fell later when compared to the first wave of labeled mitoses obtained when 3H‐TdR was injected at 21.00 hours; and (3) in both experimental groups there was a suggestion of a second wave of labeled mitoses, especially in the group injected with 3H‐TdR at 21.00 hours, where a flat second wave appeared in the region of 60–90 hr. Transit times derived from FLM curves obtained from such synchronous populations of cells are of questionable validity. Circadian rhythmicity and other causes of synchronization must be ruled out before accepting a single FLM curve as a valid indication of transit times.