Circadian rhythms in the mitotic index of the basal epithelium and in the uptake rate of 3H‐thymidine by the tongue of the rat

Abstract

AbstractCircadian rhythms are demonstrated in the tongue of adult rats for both the mitotic index of the basal epithelium and the uptake rate of injected 3H‐thymidine by the tongue tip. The animals were entrained to a light‐dark cycle for four weeks prior to the experiments with the light phase extending from 0600 to 1800 hours (CST). The daily fluctuation is approximately 300% for the mitotic index and 185% for the uptake rate of 3H‐thymi‐dine. The highest mitotic index occurs at 1100, and the highest uptake of 3H‐thymidine occurs four hours earlier at 0700. The least activity for both parameters occurs during the first part of the dark span of the light‐dark cycle. Estimates of several other rhythmic parameters are determined by a computerized method.