The predominant effect of mineralocorticoids is on the extracellu- lar balance of sodium and potassium in the distal tubule of the kidney. Aldosterone, produced solely in the zona glomerulosa, is the predominant mineralocorticoid in humans (about 50%); corti- costerone makes a small contribution to overall mineralocorticoid activity. Mineralocorticoids act on type 1 corticosteroid receptors, while glucocorticoids act on type 2 receptors, both having a very similar structure. The mineralocorticoid activity of cortisol is weak but cortisol is present in considerable excess. The mineralocorti- coid receptor in the kidney is protected from this excess by the intrarenal conversion (‘shuttle’) of cortisol to cortisone by 11βHSD type 2