![]() ![]() We have shown that transgenic mice overexpressing human PPO had reduced REM sleep compared with wild type mice indicating the importance of orexins in regulation of REM sleep and stabilization of arousal ( 11). Currently, dual orexin receptor antagonists are commercially available or under investigation for treatment of insomnia ( 10). Defects in orexin secretion result in narcolepsy in dogs, mice and humans, and orexins have been shown to have a role in stabilization of arousal ( 2– 9). Orexin-A and orexin-B, also called hypocretins, are peptides which were originally isolated from rat hypothalamus and are derived from the precursor peptide prepro-orexin (PPO) ( 1). Thereby, studies examining regulatory mechanisms and influences of OXA from blood samples should interpret results very cautiously. In conclusion, OXA is present in blood in low amounts and its levels do not follow autonomic nor neuroendocrine circadian rhythms. The OXA concentrations did not correlate to feeding nor wake/sleep, whereas cortisol, melatonin and mean arterial blood pressure presented a clear circadian rhythm in each subject. Plasma OXA levels varied between 0.5 and 16 pg/ml in seven subjects and were undetectable (below 0.5 pg/ml) in two subjects. OXA antiserum had only minor cross-reactivity with prepro-orexin precursor (<0.001%), amino-terminal peptide (<0.001%), carboxy-terminal peptide (0.001%), and orexin-B (0.3%) with high sensitivity (0.15 pg/tube). ![]() Blood pressure was monitored through the experimental period. Plasma samples were analyzed in addition for cortisol and melatonin levels. Food was served at 12 p.m, 5:30 p.m, 8 p.m and 8 a.m and the sleep time was between 10 p.m and 7 a.m. Blood samples were collected for 24 h from nine healthy males (aged 20–24 years BMI 20.7–26.5) every 2 h starting at 11 a.m. Therefore, a specific and sensitive OXA radioimmunoassay (RIA) with solid phase extraction method was developed to determine whether plasma OXA concentrations is affected by acute feeding and/or wake and sleep in young healthy males. However, reported peptide concentrations in plasma vary significantly depending on the method used. ![]() In addition to its high levels in cerebrospinal fluid, OXA is present in blood. The orexin system has been attributed to important functions in sleep, arousal and regulation of energy homeostasis. Orexin-A (OXA) has been originally isolated from a precursor peptide prepro-orexin from the lateral hypothalamus.
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