A fraction of labelled mitoses study on adrenal chromaffin tissue in the newborn mouse and the effect of hydrocortisone.

Hydrocortisone was administered to gravid mice from the thirteenth day of pregnancy until term. In vivo fraction of labelled mitoses experiments on intra-adrenal chromaffin tissue of newborn mice were performed to assess the effect of hydrocortisone on the cell cycle in this tissue. In untreated mouse intra-adrenal chromaffin tissue the total cell cycle time was 7 hours, being made up as follows: S phase 1 1/2 hours, G2 phase 1 hour, M phase 4 hours (by analysis of results, not by assumption) and G1 phase 1/2 hour (by subtraction). Hydrocortisone administration was without marked effect on these values. These results are discussed in the context of the influence of corticosteroids on the development biology of chromaffin tissue, both intra- and extra-adrenal.