Control of mineralocorticoid substitution in Addison's disease by plasma renin measurement.

In 7 out-patients with Addison's disease, plasma renin activity (PRA), plasma concentrations of angiotensin II (AT II), renin substrate (PRS), potassium, sodium and total protein, hematocrit, blood pressure, heart rate and body weight were studied after 2 weeks each on 2 mg of dexamethasone, 25 mg hydrocortisone (HC), 25 mg HC + 0.05 mg 9-alpha-fluorohydrocortisone (FC), 25 mg HC + 0.1 mg FC and 25 mg HC + 0.2 MG FC. Four further patients were less extensively studied. Mean PRA (upper normal limit, ambulatory: 12 ng AT I-ml-1-h-1) after the 5 steps of incremental substitution, starting with dexamethasone, was 192, 59, 38, 24 and 9 ng AT I-ml-1-h-1 rsp. PRS did not change with increasing substitution. PRA and AT II were significantly correlated (r = 0.91; p less than 0.0001) and proved to be the most sensitive parameters of insufficient mineralocorticoid substitution. With decreasing significance, PRA also correlated with plasma protein concentration, plasma sodium concentration (negative), delta body weight (negative), heart rate, delta mean blood pressure (negative) and plasma potassium concentration. PRA or AT II measurements are useful clinical tools to control mineralocorticoid substitution in Addisonian patients. Inappropriately high substitution can be prevented by keeping PRA in the upper normal range.