Functional adrenal zonation and regulation of aldosterone biosynthesis

Aldosterone is an important regulator of fluid and electrolyte balance. The capacity of the adrenal gland to produce aldosterone is controlled by circulating levels of angiotensin II and potassium, which regulate the expression of aldosterone synthase (CYP11B2). This enzyme catalyzes the final steps of aldosterone synthesis and is expressed only in the zona glomerulosa of the adrenal cortex. The development of new systems for in vitro studies of expression has helped to define the molecular mechanisms that regulate this enzyme and thus the capacity of the adrenal gland to produce aldosterone. Both potassium and angiotensin II increase intracellular calcium levels, which regulate expression of CYP11B2 through transcription factors that interact with defined sites in the 5'-flanking region of the gene.