Behaviour of the Proliferative Compartment of the Small Intestine at Different Times of the Day

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Abstract
The modifications of mitotic and labelling indices in animals killed at different hours of the day were analysed. The invertase activity was also assayed. This brush border enzyme, synthetized by the differentiating cells, showed a clear circadian rhythm with a maximum in the night and a minimum near the end of the light period. Mitotic and labelling indices showed the highest activity in the night and at noon. The positions of mitotic and labelled epithelial cells in the crypt were also determined. The frequency of labelled cells in the different positions of the crypt evidenced a shift of these cells towards the crypt-villus junction in the late afternoon with a consequent reduction of the differentiating compartment.