Influence of the Circadian Rhythm in Cell Division on Radiation-Induced Mitotic Delay in Vivo

Abstract

RUBIN, N. H. Influence of the Circadian Rhythm in Cell Division on Radiation-Induced Mitotic Delay in Vivo. Radiat. Res. 89, 65-76 (1982). Mitotic delay is described as a classical response to radiation; however, circadian rhythmicity in cell division in vivo has not been considered by many authors. The present study investigated the relation between fluctuations reported as mitotic delay and recovery in vivo and circadian oscillations in mitotic index in mouse corneal epithelium. One aspect involved single doses (approximately 600 rad) given to mice at different circadian stages. The normal circadian rhythm in cell division was never obliterated. Inhibition of mitosis was evident but unpredictable, ranging from 6 to 15 hr after irradiation. Recovery was evident only during the daily increase in mitotic index of controls. The classical interpretation of recovery from mitotic delay may be an in vitro phenomenon not reflecting in vivo responses, which are apparently strongly circadian stage dependent. The second portion of the study demonstrated a doseresponse effect on length of mitotic delay and, to a lesser extent, degree of recovery.