Immunoreactive orexin-A in human plasma

Orexin-A and orexin-B are newly discovered neuropeptides which art: implica ted in feeding behavior and arousal state. We studied immunoreactive(IR)-or exin-A concentrations in human plasma by radioimmunoassay. IR-orexin-A conc entrations in plasma obtained from 17 healthy subjects in the morning were 1.94 +/- 0.24 pmol/liter (mean ir SEM). IR-orexin-A levels in the plasma ob tained at night were not significantly different from those obtained in the morning in 9 female subjects. The HPLC analysis of the plasma extract show ed two immunoreactive peaks; one peak eluting in an identical position to s ynthetic orexin-A, and one eluting earlier. This study has shown for the fi rst time the presence of orexin-A in human plasma. (C) 2001 Elsevier Scienc e Inc. All rights reserved.