Ontogenesis of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase in the rat adrenal as revealed by immunocytochemistry and in situ hybridization.

The enzyme 3 beta-hydroxy-5-ene-steroid dehydrogenase/5-ene-4-ene isomerase (3 beta-HSD) catalyzes an essential step in the biosynthesis of all classes of active steroids, namely glucocorticoids, mineralocorticoids, progesterone, and sex steroids. To obtain further information on the expression and localization of 3 beta-HSD during development in the rat adrenal, two complementary cytochemical techniques were used: immunocytochemical localization with antibodies against purified human placental 3 beta-HSD, and 3 beta-HSD messenger RNA localization achieved by in situ hybridization with a rat 3 beta-HSD complementary DNA probe. During foetal development, the first detection of 3 beta-HSD messenger RNA was achieved on day 16 by in situ hybridization, the silver grains being located on the cortical cells. Between days 17 and 20, on the other hand, immunostaining became positive in the cytoplasm of the same cortical cells, the capsule being negative by both immunostaining and in situ hybridization. Interestingly, two distinct zones of intensity of 3 beta-HSD localization could be distinguished, namely the highly labeled reticular and fascicular zones and the less positive glomerular zone. This observation coincides with the onset of fetal ACTH secretion on days 17-18 and with accelerated adrenocortical growth and differentiation. After birth and until day 25, strong immunolabeling was observed in the cytoplasm of adrenocortical cells, the glomerular zone being labeled at a lower degree than the remaining cortex. The same localization was obtained by in situ hybridization. This low labeling of the glomerular zone might be related to the low plasma levels of angiotensin II observed in the immature rat. From day 25 after birth, the three zones of the cortex were uniformly labeled and no immunostaining was seen in the medulla or capsule. Similarly, by in situ hybridization, silver grains were located exclusively in the adrenal cortex. The present data suggest that 3 beta-HSD expression could well play a major role in regulating adrenal function during foetal and postnatal development.