Regulation of aldosterone biosynthesis: the end of the road?

1. Because aldosterone is the minority hormone of the adrenal cortex, its proper function depends on protective physiological mechanisms. These include a particular site of aldosterone biosynthesis in the zona glomerulosa of the adrenal cortex as well as a complex multifactorial control system, which adapts aldosterone production to acute and chronic changes in body sodium and potassium content, irrespective of pituitary adrenocorticotropic hormone (ACTH) secretion. 2. Over the past decade, an important element of these mechanisms has been identified in the form of the enzyme involved in the final steps of aldosterone biosynthesis. In species such as the human, rat and mouse, the conversion of deoxycorticosterone to aldosterone is catalysed by an isozyme (CYP11B2) of cytochrome P450(11) beta (CYP11B1). The gene encoding this enzyme is expressed only in the zona glomerulosa. Its transcription is enhanced by sodium deficiency and potassium intake, but is suppressed by long-term administration of high doses of ACTH. 3. In contrast, the gene encoding CYP11B1 (i.e. the major (non-aldosterone-producing) type of the enzyme) is expressed mainly in the zona fasciculata and its expression depends on physiological concentrations of ACTH. 4. In other animal species (cattle, pig, sheep), the major forms of cytochrome P450(11) beta have an inherent aldosterone-synthesizing activity, which is, however, selectively suppressed in mitochondria of zona fasciculata cells. 5. The elucidation of the mechanisms involved in this suppression or of those mediating alterations in CYP11B2 expression in response to physiological stimuli may be important areas of future research on the regulation of aldosterone biosynthesis.