The effect of hydrocortisone on the para-aortic body of the newborn mouse: an in vivo fraction of labelled mitoses study.

Information about the cell cycle of the mouse para-aortic body within the first 24 hours of postnatal life was derived from a fraction of labelled mitoses study. The total cell cycle time was 8 1/2 hours, being made up as follows: S phase-2 hours; G2 phase-1 hour; M phase-3 1/2 hours (by analysis of the results, not by assumption) and G1 phase-2 hours (by subtraction). Problems are discussed regarding the length of G2 and M phases and the consequences for G1. After hydrocortisone administration (40 mg/kg/day) to female mice for the last seven days of pregnancy, the pattern in newborn mice was disrupted. Values for G2 and M were similar to those of the untreated group, but no values were obtainable for the other phases of the cell cycle or for the total cell cycle time. These results after hydrocortisone treatment could be explained by the superimposition of the cell cycles of two or more different groups of cells. They are discussed with regard to the life span of the para-aortic body, and their implications are considered in the light of previously reported glucocorticoid-induced transformations of small granule cells from cervical sympathetic ganglia into catecholamine-storing chromaffin cells. The established hyperplastic effect of hydrocortisone on the para-aortic body is therefore not the result simply of an acceleration of the cell cycle, but it may involve the incorporation into the proliferative compartment of cells previously either moribund or nonproliferating.