Regulation of Aldosterone Secretion

Regulation of aldosterone secretion is complex both in terms of the number of secretagogues that can influence its biosynthesis and the number of second messengers utilized by these secretagogues (Table 1, Figure 1). ACTH primarily acts via the adenylate cyclase system through a stimulatory G protein; however, there is evidence that at low concentration it may also activate calcium influx and phospholipase C in some species. The primary effect of AII is activation of phospholipase C, which increases both calcium release from intracellular stores and calcium flux across the cell membrane and activates protein kinase C. Potassium depolarizes the membrane, thereby activating calcium flow through voltage-dependent calcium channels. It also directly or indirectly causes release of calcium from intracellular binding sites. A small change in cAMP levels may also be involved in the sustained secretory response to potassium. Species variation in the regulation of aldosterone secretion probably exists; the control mechanisms in the human appear to be closer to those in the rat than to those in cow and sheep. How changes in dietary sodium and potassium modify aldosterone secretion and the adrenal's responsiveness to secretagogues remains unclear. Yet these effects may be of considerable importance, both in terms of understanding the overall regulation of aldosterone secretion and in resolving the discrepancies in the results obtained under different experimental conditions.