24-HOUR RHYTHM IN THE MITOTIC ACTIVITY OF A GRAFTED MAMMARY CARCINOMA IN FEMALE C3H-MZA MICE ON NORMAL AND INVERTED LIGHTING REGIMENS.

Abstract

SYNOPSISThe existence of a 24‐hour rhythm in the mitotic activity of histologically‐selected zones of a mammary carcinoma, grafted in female C3H/Mza subjected to a regular illumination schedule (6 a.m. to 6 p.m.) is demonstrated.Inverting the periodicity of illumination conditions (6 p.m. to 6 a.m.) leads to a shift in the times of maximal and minimal mitotic activity.On both illumination schedules, the maxima of the mitotic activity are observed during the light period (rest) and the minima during the dark period (activity); this demonstrates that light is the factor responsible for the rhythm with both illumination schedules and excludes the hour of the day as such.Results of other authors and the possible mechanisms involved in the production of this rhythm are discussed.