In order to clarify the diurnal pattern of secretion of plasma immunoreactive (IR) proopiomelanocortin (POMC)-derived peptides, IR-N-terminal peptide (Nt), IR-β-endorphin (Ep), IR-β-lipotropin (LPH), and IR-ACTH (ACTH) in normal subjects and in patients with Adisson's disease and Cushing's disease, we measured these 4 peptides in the same plasma obtained at 0900 h and then every three hours until 0600 h at the next day.
All four peptides showed diurnal rhythms with the peaks at 0600 h, and the nadirs of ACTH, LPH, Ep and Nt were at
0000
h,
0000
h, 1800 h and 0300, respectively in normal subjects. In patients with Addison's disease, these four peptides also showed diurnal rhythms with the peaks at 0600 h for ACTH and Ep and at 0900 h for LPH and Nt, and the nadirs at 2100 h for ACTH and Ep and at
0000
h for LPH and Nt. The molar ratios of Ep/ACTH, LPH/ACTH and Nt/ACTH in plasma also presented diurnal variations in normal subjects and in patients with Addison's disease. On the other hand, in patients with Cushing's disease, ACTH, LPH and Nt showed no rhythmicity or change in molar ratios of Ep/ACTH, LPH/ACTH or Nt/ACTH. Only Ep showed diurnal variation. The molar ratios of Ep/ACTH, LPH/ACTH and Nt/ACTH in patients with Cushing's disease were significantly higher than those in normal subjects and in patients with Addison's disease at
0000
h In patients with Cushing's disease, the molar ratios of Ep/ACTH, LPH/ACTH and Nt/ACTH differed in each case and there was no remarkable change in these molar ratios during the 24 hours of a day. These phenomena might be in part due to different half-lives of POMC derived peptides and/or different processing of POMC in each case or at each time during a day.
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