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Circadian rhythms of DNA synthesis, mitotic activity, and duration of mitosis in rat liver were studied on postnatal days 3, 7, and 12. Some age-related peculiarities of these rhythms were revealed. Epidermal growth factor was found to play an important role in the formation of cell proliferation rhythm during the early postnatal ontogeny and in the regulation of the pool of proliferating hepatocytes.

Numbers of mitoses and of colchicine mitoses, and the duration of mitosis in corneal and tongue epithelium as well as in hepatocytes of intact and adrenalectomized rats have been studied in dynamics within 24 hours. In the control animals, the 24 hours rhythm of mitotic activity and the duration of mitosis were established. The length of mitosis falls during the high rate mitotic activity to increase when the number of dividing cells is reduced. Adrenalectomy results in decreasing the amplitude of mitotic activity fluctuations and in diminishing the amount cells entering mitosis during the 24 hours period. The rate of physiological regeneration in tissues of adrenalectomized animals is reduced. Different sensibilities of investigated tissues to adrenal cortex hormones deficiency have been revealed.

In corneal epithelium of CBA mice the index of colchicine mitoses diminished after splenectomy in the day period characterized by rising mitotic activity in control animals. The duration of active phase of cell division rhythm shortened while the maximum of mitotic activity delayed in comparison with control animals. The total amount of cells entering mitosis during 24 hours diminished by 27.7% and the rate of physiological regeneration of corneal epithelium decreased.

In experimental hypercorticism the average daily concentration of glucocorticoids in blood plasma is 4 times higher than in control one, the amplitude of the circadian rhythm increases almost 3 times, the time of maximum concentration does not change. The adrenocorticotrophic hormone (ACTH) average circadian concentration decreases twofold. The adrenalectomy results in abrupt smoothing down of the circadian rhythm of glucocorticoids concentration and in increasing (in 2,4 times) of the average circadian concentration of ACTH. The pattern of circadian rhythm remains, however the acrophase of hormone secretion is shifted. The circadian rhythm of cells devision in esophagus epithelium changes. The maximum of mitotic index is absent in adrenalectomized rats and the amplitude of its circadian variations decreases. In experimental hypercorticism the biphase rhythm of mitoses in induced.

The diurnal changes of mitosis and DNA-synthesizing cells count in the tongue epithelium of intact and adrenalectomized mice were studied. A partial desynchronization of mitotic division, as well as diminution of mitotic index variation amplitude and prolongation of high mitotic activity were observed in the operated animals in the course of 24 hours. The average 24-hour mitotic index in the basal layer of the tongue epithelium was the same in the intact and the operated animals. The rhythm of the DNA synthesis failed to differe from control. Thus, adrenalectomy in mice led to distrubances of the diurnal mitotic rhythm in the tongue epithelium, but had no effect on the rhythm of the DNA synthesis and the level of the proliferative activity.

Bilateral subdiaphragmatic vagotomy in rats 7 days after surgery results in increasing proliferative activity of the jejunum epithelium not changing circadian rhythm of the mitotic process. Vagotomy induces changes in the diurnal rhythm structure of DNA-synthesis in the jejunum epithelial cells, i.e. monoapical rhythm in the norm becomes biapical.