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A method for the simultaneous determination of the metabolic clearance rate (MCR) and plasma concentration of aldosterone is described. From these 2 parameters the blood production rate (secretion rate) of aldosterone was calculated. Using this approach the effect of posture on aldosterone secretion and metabolism was studied in 18 normal male subjects, 3 patients with primary aldosteronism and 1 anephric subject. After sitting, there was no significant change in the MCR. The plasma concentration of aldosterone increased 6-fold and the blood production rate increased 5-fold. After standing, the MCR decreased significantly by 23%. The plasma concentration increased 10-fold and the blood production rate increased 8-fold. These results indicate that the increase in secretion rate rather than the decrease in MCR is the major factor regulating plasma aldosterone concentration. All 3 patients with primary aldosteronism had an elevated plasma aldosterone concentration in the supine state, and a correspondingly elevated blood production rate. After standing, they all showed an increase in plasma concentration and blood production rate, but these changes were not as marked as in normal subjects. The anephric patient had a high normal plasma aldosterone concentration in the supine state, but failed to respond to the postural stimulus. The significance of these findings and possible use of this approach in studying pathologic states are discussed.
BALIKIAN et al. (Fri,) studied this question.