Circadian Rhythm in Circulating Concentration of Dihydroxyphenylacetic Acid in Normal Women*

Publisher Website
Google Scholar
Abstract
The 24-h patterns of plasma concentration change in dopamine (DA) and its immediate deaminated metabolite, dihydroxyphenylacetic acid (DOPAC), were determined in 6 normal women (16 studies) by a modified radioenzymatic assay. Changes in DOPAC levels exhibited a marked circadian rhythm, with a peak during the day and a nadir at night. At 1200 h, the DOPAC concentration increased significantly (P < 10-4) to a peak value (62.9 .+-. 8.4 ng/ml) 117% higher than the 24-h mean. At 2200 h, plasma DOPAC decreased (P < 10-4) to a nadir concentration (10.0 .+-. 3.3 ng/ml) 66% lower than the 24-h mean. The circadian rhythm of DOPAC could be reproducibly demonstrated over at least 4 successive days in individual subjects. There were no well defined circadian variations in plasma concentrations of DA. Since the plasma DOPAC concentration appears to reflect CNS dopaminergic neuronal activity, the present demonstration of a circadian rhythm of plasma DOPAC suggests that the activity of CNS DA-containing cells is higher during the day than at night.