Effects of exogenous ACTH on the rat fetal adrenal cortex: a histochemical and electron-microscopical observation.

ACTH was administered subcutaneously to rat fetus directly at the late stage of fetal development and acute reaction on the fetal adrenal cortex was observed histochemically and electron microscopically. By administration of ACTH the adrenal cortex became remarkably hyperemic and there were swollen cells in all layers, particularly in the middle and inner layers (corresponding to the zona fasciculata and reticularis in adult rat). Marked reduction of lipid, enlarged mitochondria with increased vesicular cristae and increased smooth-surfaced endoplasmic reticulum (SER) were characteristic. The alterations of mitochondria preceded the change of SER, and thereafter mitochondria showed rapid degeneration. The outer layer (corresponding to the zona glomerulosa in adult rat) also showed similar changes by ACTH to those of the other two layers. These results indicated that the fetal adrenal cortex of rats was exogenous ACTH-reactive and its reaction which was different from that of adult cortical cells, seemed to be specifically related to the development and differentiation of the cells.