STUDIES ON MECHANISM OF DIURNAL-VARIATION OF PROLIFERATIVE INDEXES IN SMALL BOWEL MUCOSA OF RAT

In the rat small bowel mucosa significant variation was found in both the labeling and the mitotic indices with time of day. The zenith and the nadir of labeling and mitotic activity coincided at 15.00 and 02.00 h, respectively. Small changes were found in the cut-off position, but this variation in proliferative compartment size was insufficient to account for the comparatively wider fluctuations in proliferative indices. Measurements of the rate of entry into mitosis, using metaphase arrest with vincristine at 3 widely separated times during the day, showed no significant change. Changes in the growth fraction or in the birth rate as measured cannot account for diurnal variation in the proliferative activity of the small bowel mucosa. A hypothesis which involves diurnal fluctuations in the transit times through G1 and G2 was proposed.