A study of mitotic activity and the diurnal variation of the epithelial cells in wounded rectal mucous membrane.

Excision ulcers of the rectal mucous membrane were made in two groups of rats. One group was wounded at 09.00 hours and the second group at 21.00 hours. Mitotic counts were carried out in the glandular epithelium at the ulcer edges at 2 hour intervals over a period of 24 hours. Mitotic activity increased in 2-4 hours and thereafter showed a peak-and-trough pattern. The wounded rectal epithelial cells exhibited a diurnal variation with a peak of activity during the day and a low period of activity at night. It would seem unlikely that the adrenaline-chalone complex acts on the rectal epithelium, as this would entail maximal mitotic activity during periods of rest, when the circulating levels of adrenaline in the rat are at their lowest. The experiments clearly showed that the diurnal variation was not abolished by wounding. The increased mitotic activity occurred in the epithelial cells in the lower and mid thirds of the colonic glands; dividing cells were rarely seen in the top twenty cells or so of the glands, or in the surface epithelium. Mitotic activity was often lower in the first one or two glands at the immediate wound edge, which is difficult to explain by present theories of mitotic control.