Autoradiographic studies of the diurnal rhythm of the cell proliferation in the adrenal cortex of the rat.

With the aid of the autoradiographic technique we examined the question of diurnal or circadian rhythm of the cell proliferation as well as the mitotic rate in the three zones of the adrenal cortex of the rat. To evaluate the diurnal rhythm it is necessary to run experiments within 24-hour intervals. In order to examine observed variations as to their reproducibility we prolonged our investigations over a period of 72 hours. The proliferation activity as well as the mitotic rate in the zona glomerulosa show no diurnal rhythm. This is not so in the zona fasciculata. Here we find a correlated circadian rhythm for both parameters.