Sleep deprivation (SD) is a growing hazard through its effects on metabolism.Orexin is involved in regulation of both sleep and metabolism. Work on orexin receptors may explainthe mechanisms of some hazardous effects of SD. Aim:To test the role of orexin-1 receptor (OX1R)blocker, SB-334867 in changes of triglycerides and cholesterol metabolisminduced by SD. Method: 72 adult albino rats arranged in 4 equal groups: control, SD, SD-OX1R blocked &SD-DMSO groups. The 3 SD groups are subjected to 8

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... ys of paradoxical SD using the modified multiple platform method. The OX1R blocked group was injected intraperitoneallydaily with single dose (3 mg/kg/day) of SB-334867 dissolved in 2 ml DMSOand diluted 1:1000. The SD-DMSO group was injected by 2 ml of DMSO diluted 1:1000. Triglycerides and cholesterol levels weremeasured. Results: Blood triglyceride levels dropped in all groups subjected to SD after the 1 st day while the blood cholesterol level dropped in all groups subjected to SD at the 7 th or 8 th day. In SD-OX1R blocked group showed less drop in blood triglyceridesthan the other SD groups but statistically non-significant change in cholesterol level. Conclusion: SDleads to earlier and more dropin blood triglyceridesthan the drop in cholesterol levels. This can be explained by high metabolism during SD with dependence on triglyceride more than cholesterol. OX1R blocker partially reduces the drop of triglyceride not cholesterol level indicating that orexinmay be involved in control of triglyceride metabolism but not cholesterol.