The effect of in vivo hydrocortisone administration on the labelling index and size of the intra- and extra-adrenal chromaffin tissue of the fetal and perinatal mouse.

Administration of hydrocortisone in vivo to pregnant mice between the eighth and sixteenth days of gestation leads to highly significant increases in both the volume and the labelling index of extra-adrenal chromaffin tissue (as represented by the para-aortic body) of 16 days fetal mice. The labelling index of intra-adrenal chromaffin cells increases slightly after hydrocortisone administration, but the volume of the adrenal chromaffin tissue was not assessed since the groups of chromaffin cells had not in all cases aggregated to form a distinct medulla. Hydrocortisone administration to mice for the last week of gestation also leads to a highly significant increase in the size and the labelling index of the perinatal para-aortic body. Although an increase in the labelling index of perinatal intra-adrenal chromaffin cells is brought about, this is much less marked than that of the extra-adrenal tissue and neither is it reflected by any increase in the volume of the now discernible adrenal medulla. These increases in size and labelling index of the para-aortic body constitute a hyperplastic response rather than a hypertrophic response. Various possible mechanisms and implications are discussed in the light of the development of chromaffin tissue and the effects of the cortex and its secretions on the medulla. Associated effects of hydrocortisone noted in this work are the resultant marked diminution of adrenocortical volume in the perinatal gland, and a slight fall in the labelling index of perinatal intra-adrenal haemopoietic cells.