Circadian rhythm in the rate of cellular proliferation and in the size of the functional compartment of mouse jejunal epithelium

Abstract

Circadian variation in the small bowel mucosa of male Balb/c mouse was studied. The labelling index was studied at 2 hourly intervals throughout a 24 h period by using autoradiographic techniques with³HTdR. A 12 h light-dark schedule was employed. Villus and crypt cell populations, together with the mitotic index, were studied using the micro-dissection technique. Growth fractions were determined from the labelling index distribution curves. The peaks in both villus and crypt cell population occurred during the day, with maximum villus population of 3,887 cells/villus at 13.00 h and maximum crypt population of 178 cells per crypt at 09.00 h. The peaks of labelling index (I _s) and mitotic index (I _m) occurred during the dark period. The peak value ofI _s 38% at 17.00 h–19.00 h, was about 6–8 h in advance of the peak value ofI _m (6%). The peak in growth fraction corresponded to that of the labelling index.