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Histological and functional characteristics of the fetal human adrenals was studied in 119 normal fetuses aged 12 to 36 weeks development (WD). Immunocytochemical detection of steroidogenesis enzyme (3beta-HSD and P450 c21) and evaluation of cell proliferation using two nuclear markers (Ki-67 and PCNA) were performed in 70 of them. The human fetal adrenal cortex is composed of two morphologically distinct zones: the definitive peripheral zone and the fetal inner zone. From the 12th WD, we observed expression of an adherence protein (NCAM) and two steroidogenesis enzymes (3beta-HSD and P450 c21) in the definitive zone cells, attesting to the capacity of these cells to synthesize mineralocorticoids and/or cortisol. In the fetal zone, only P450 c21 immunoreactivity was detected. From the 14th WD, a transitional zone between the definitive zone and the fetal zone was identified by immunocytochemistry, with expression of 3b-HSD from the 21st WD. Only cells of the definitive zone proliferated from the 12th to 25th WD. The indexes of proliferation of PCNA and Ki-67, 40% and 25% respectively, decreased gradually and were lower than 1% at the 25th WD.

Granulosa cells harvested from cavitary follicles of varying diameters have been cultivated in vitro in basic conditions and in presence of HCG, and then tested for the activity of steroid-3 beta-ol-dehydrogenase and observed with a scanning electron microscope. As concerns the enzymatic activity, the cells of the smaller follicles (5--6 mm) show a very low reactivity which increases in presence of HCG. In the cells of the larger antral follicles (8--9 mm) the reactivity is remarkably higher, particularly when HCG is added to the medium. With the scanning electron microscope the appearance of the granulosa cells of the larger follicles cultivated with HCG is very peculiar because of the presence on the cell surface of many cytoplasmic evaginations. These are more numerous and thinner than those normally found on the uncultured cells and on the cells cultivated in basic conditions.

With the potassium ferricyanide method, the localization of the sites of 3 beta-hydroxysteroid dehydrogenase activity has been investigated in the glandular tissue cells, previously fixed, of the Pleurodeles testis. An abundant copper ferrocyanide precipitate, the final reaction product, is observed in the vicinity of the external faces of the membranes of the smooth endoplasmic reticulum, or in contact with them. A very weak reaction occurs in mitochondrial cristae.