The average secretion rate of aldosterone is 100-200┬╡g/d (Fig. 7.14). It is only weakly bound to plasma proteins and thus has a relatively short half-life (twenty minutes) and a high metabolic clearance rate (1500l/d). Both the liver and kidney are sites of metabolic clearance, and only a small percentage of aldosterone is excreted unchanged in the urine. A measurement of plasma aldosterone levels, or an estimation of the levels of the metabolite 18-glucuronoside, is commonly used in clinical situations. Diet, posture, and time of day affect aldosterone secretion and must be adequately controlled to permit interpretation of results.
