Circadian rhythm of the angiotensin converting enzyme (ACE) activity in serum of healthy adult subjects.

Angiotensin converting enzyme (ACE) activity was measured in the peripheral serum of 10 healthy, diurnally-active and nocturnally-resting adult subjects (5 women and 5 men). Blood was drawn serially at 4-h intervals throughout a 24-h cycle with the subjects hospitalized and synchronized. They were not kept in recumbency. Data were evaluated by conventional statistical analysis and by single- and population mean- cosinor procedures. A low-amplitude circadian rhythm was statistically validated for the group. Acrophase was located in the afternoon, at about 1630. The recognition that ACE activity oscillates physiologically in the peripheral blood according to a circadian rhythm may serve to amplify the clinical use of ACE measurements.