[The mechanisms of corticoids biosynthesis revealed by immunohistochemistry and in situ hybridization]

Abstract

The improvement of immunohistochemistry and in situ hybridization techniques has recently allowed a prominent advancement in morphological research on the mechanisms of steroid-hormone biosynthesis in the adrenal gland. Cholesterol side-chain cleavage enzyme (P450scc) was localized in the inner mitochondrial membrane of all cortical cells. Steroid 3 beta-hydroxysteroid dehydrogenase/delta 5-4-isomerase (3 beta-HSD) and 21-hydroxylase (P450c21) were present in the membrane of smooth endoplasmic reticulum (SER) of all cortical cells. 17 alpha-Hydroxylase/C17-C20 lyase (P45017 alpha) was located in the SER membrane of the zona fasciculata-reticularis cells of human, bovine, swine, guinea-pig, and hamster adrenal gland. This enzyme, however, was absent in the adrenal gland of rat, mouse and rabbit. 11 beta-Hydroxylase (P45011 beta) and aldosterone synthase (P450aldo) were situated in the inner mitochondrial membrane of the zona fasciculata-reticularis cells and in that of the zona glomerulosa cells, respectively. These results indicate that aldosterone is synthesized in the zona glomerulosa cell, and that glucocorticoids such as cortisol and corticosterone are synthesized in the zona fasciculata-reticularis cells. The conversion of cholesterol to pregnenolone and the final steps of corticoids synthesis occur in the mitochondria, while the intermediate steps, leading to the synthesis of deoxycorticosterone or deoxycortisol from pregnenolone, take place in the SER membranes.