Diurnal rhythm of plasma immunoreactive corticotropin-releasing factor in normal subjects

Abstract

Plasma corticotropin-releasing factor (CRF), corticotropin (ACTH) and cortisol levels were simultaneously determined by radioimmunoassays at 0600h, 1200h, 1800h and 2200h in six normal subjects, in order to examine whether the diurnal rhythm in plasma CRF exists and how it correlates to the diurnal rhythm in plasma ACTH and cortisol concentration. The highest CRF level was observed at 0600h (7.0 ± 1.2 pg/ml) and significantly lower levels (p<0.01) at 1800h (1.7 ± 0.2 pg/ml) and 2200h (1.9 ± 0.4 pg/ml). A clear diurnal rhythm was demonstrated in plasma ACTH and cortisol levels, with the highest values at 0600h (44.6 ± 8.1 pg/ml and 15.9 ± 2.0 μg/dl, respectively) and the lowest at 2200h (12.3 ± 2.8 pg/ml and 4.6 ± 1.0 μg/ml, respectively). These results suggest that the diurnal rhythm in ACTH and cortisol is under the regulation, at least in part, of the diurnal rhythm in CRF secretion.