Differentiation and proliferation of adrenocortical cells during the early stages of regeneration.

Changes in the adrenal cortex of the rat were studied by stereologic and autoradiographic techniques during the early phases of regeneration. The adrenal cortex was enucleated on the left side, the right kidney and adrenal gland were removed, and rats were given 1% sodium chloride as drinking solution according to the procedure for inducing adrenal regeneration hypertension. The growth of adrenocortical cells during early stages of regeneration can be divided into two phases. During the first stage (0 to day 3), the cells remaining attached to the capsule recovered from trauma and began to differentiate from zona glomerulosa-like to those characteristic of the zona fasciculata. Mitochondria also divided, and there was increased surface area per cell of total mitochondrial membranes. The number of cells decreased in this initial phase, although the average cell volume increased, in preparation for mitotic division. This conclusion is supported by an increase in the percentage of cells labeled with 3H-thymidine at day 3. The second period (end of day 3 to day 7) was a proliferative phase reflected in a large number of labeled cells and a maximal number of grains per volume (reflecting activity of 3H-thymidine incorporation) followed by a blunting of the wave of proliferation at day 7. As cells divided, the total mitochondrial membranes and cristae per cell decreased. The first week after enucleation is characterized first by preparation for cell division, and in the second phase of the first week a wave of proliferation occurs. At the end of the first week, fewer labeled cells were seen, and there was a decrease in cristae membranes.