No abstract

The adrenal glands are the primary source of mineralocorticoids, glucocorticoids and the so-called adrenal androgens. Under physiological conditions, cortisol and adrenal androgen synthesis are controlled primarily by adrenocorticotrophic hormone (ACTH). Although it is well established that ACTH can stimulate steroidogenesis in the human adrenal gland, the effect of ACTH on overall production of different classes of steroid hormones has not been defined. In this study, we examined the effect of ACTH on the production of twenty-three steroid hormones in adult adrenal (AA) primary cultures and 20 steroids in the adrenal cell line, H295R. Liquid chromatography/tandem mass spectrometry analysis (LC-MS/MS) revealed that in primary cultures that cortisol and corticosterone were the two most abundant steroid hormones produced with or without ACTH treatment (48 h). Cortisol production responded the most to ACTH treatment, with a 64-fold increase. Interestingly, the production of two androgens, androstenedione and 11β-hydroxyandrostenedione, that were also produced in large amounts under basal conditions significantly increased after ACTH incubation. In H295R cells 11-deoxycortisol and androstenedione were the major products under basal conditions. Treatment with forskolin increased the percentage of 11β-hydroxylated products including cortisol and 11β-hydroxyandrostenedione. This study illustrates that normal adrenal cells respond to ACTH through the secretion of a variety of steroid hormones, thus supporting the role of adrenal cells as a source of both corticosteroids and androgens.

The adrenal glands are the primary source of minerocorticoids, glucocorticoids and the so-called adrenal androgens. Under physiological conditions cortisol and adrenal androgen synthesis are controlled primarily by adrenocorticotrophic hormone (ACTH). Although it has been established that ACTH can stimulate steroidogenesis, the effects of ACTH on overall gene expression in human adrenal cells have not been established. In this study, we defined the effects of chronic ACTH treatment on global gene expression in primary cultures of both adult adrenal (AA) and fetal adrenal (FA) cells. Microarray analysis indicated that 48 h of ACTH treatment caused 30 AA genes and 84 AA genes to increase by greater than 4-fold, with 20 genes common in both cell cultures. Among these genes were six encoding enzymes involved in steroid biosynthesis, the ACTH receptor and its accessory protein, MRAP (ACTH receptor accessory protein). These data provide a group of ACTH-regulated genes including many that have not previously been studied with regard to adrenal function. These genes represent candidates for regulation of adrenal differentiation and steroid hormone biosynthesis.

The human adrenal gland directly secretes small, but significant, amounts of testosterone that increases in diseases of androgen excess. AKR1C3 is expressed in the human adrenal gland, with higher levels in the zona reticularis than in the zona fasciculata. AKR1C3, through its ability to convert androstenedione to testosterone, is likely responsible for adrenal testosterone production.

Very low-density lipoproteins (VLDL) are a class of large lipoprotein synthesized in the liver. The key function of VLDL, in vivo, is to carry triglyceride from the liver to adipose tissue. As a steroidogenic organ, the adrenal gland mainly uses lipoproteins as sources of cholesterol. Although VLDL receptors have been detected in the human adrenal, the function of VLDL in the adrenal gland remains unknown. Herein, we used primary cultures of human and bovine adrenal cells and the adrenocortical cell line H295R as models to determine the effects of VLDL on adrenal steroidogenesis. Our studies revealed that VLDL significantly increased aldosterone synthesis in all of the models tested. This increase was largely due to VLDL's stimulation of the expression of steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2). VLDL increased CYP11B2 mRNA expression in a concentration-dependent manner. Effects of VLDL on CYP11B2 transcript levels were not additive with angiotensin II or potassium but were additive with the cAMP pathway agonists ACTH and forskolin. Nifedipine completely inhibited the effects of VLDL on CYP11B2 mRNA, suggesting that calcium is the main signal transduction pathway used by VLDL in adrenal cells. Indeed, VLDL increased cytosolic free calcium levels. An in vivo study conducted in sucrose-fed rats showed a positive correlation between elevated triglyceride (VLDL) levels in plasma and CYP11B2 expression in the adrenal. In conclusion, we have shown that VLDL can stimulate aldosterone synthesis in adrenocortical cells by increasing StAR and CYP11B2 expression, an event likely mediated by a calcium-initiated signaling cascade.