Integrated concentration of plasma aldosterone in normal subjects: correlation with cortisol

The integrated concentration (I. C.) of plasma aldosterone and cortisol was determined every 30 min during a 24-h period, using a blood collection system composed of a nonthrombogenic catheter and a small, portable withdrawal pump. The experiments were carried out in 8 normal adult men during daily routine life, and repeated in 2 of the subjects while recumbent in bed most of the day. The following conclusions were made: a) The 30-min I. C. of aldosterone fluctuated widely throughout the day. b) Although peaks of increased concentration occurred after a change in posture from supine to erect, there were many peaks of concentration that occurred during the supine posture. The 24-h I.C. of aldosterone in 2 subjects that were studied a second time while staying in bed most of the day was lower than the I. C. observed during normal activity. Furthermore, there was a significant correlation between 24-h I. C. and percentage of time spent in supine position. c) A weak, but significant correlation was found between the 30-min I. C. of aldosterone and cortisol in 4 out of the 7 subjects tested. The overall correlation for all experiments was also significant (R = 0.3. p smaller than 0.001). D) The 4-h I. C. of aldosterone and cortisol showed that the lowest mean values were between 4 PM and 4 AM and the highest values between 4 AM and 4 PM for both steroids.