SPECIFIC REGULATION OF STAR EXPRESSION IN THE RAT ADRENAL ZONA GLOMERULOSA - AN IN-SITU HYBRIDIZATION STUDY

Steroid acute regulatory protein (StAR) plays an essential role in ste roidogenesis because it is responsible for the transfer of cholesterol from cellular stores to the inner mitochondrial membrane. We investig ated the distribution and regulation of StAR expression in association with aldosterone production in the rat adrenal gland in vivo. Using n onradioactive in situ hybridization, we demonstrate that the outermost five to seven parenchymal cell layers express the StAR gene only weak ly and inhomogeneously. The strongest expression is found in the zona fasciculata and zona reticularis. In addition, some cells in the adren al medulla also stained positively. To differentiate between functiona lly active glomerulosa and inactive intermediate cells, we compared th e expression pattern of StAR with that of aldosterone synthase. The ex pression of the latter is localized to two or three cell layers only, located immediately below the capsule. However, the cells of the inter media are capable of expressing both genes prominently, as shown after stimulation with bilateral nephrectomy for 2 days. All zones of the a drenal cortex by then expressed StAR gene to the same extent. This was accompanied by a 50-fold elevated plasma aldosterone concentration. O ur data demonstrate that the width of the aldosterone-producing zone c an increase within a short period of time by recruiting hormonally ina ctive cells to steroidogenesis.