Diurnal rhythms of cell reproduction and of some morphometric indices in the thyroid gland of young rats.

Abstract

Monophasic diurnal rhythms of mitosis and DNA synthesis are characteristic of the thyroid gland epithelium of young rats (unlike adults). It is postulated that the diurnal rhythm of mitotic activity is under the influence of a mechanism synchronizing the cell population before mitosis. With an increase in thyrocyte differentiation the number of mitoses and of DNA-synthesizing cells falls. Diurnal changes in the duration of mitosis affect the dynamics of the diurnal rhythm of mitotic activity. Changes in the height of the follicular cells during the 24-hour period are evidence of a diurnal rhythm of thyroid function in young rats.