Acute Hemorrhagic Stress in Conscious Sheep Elevates Immunoreactiveβ-Endorphin in Plasma but Not in Cerebrospinal Fluid*

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Abstract
The effects of acute hemorrhagic stress on the concentrations of immunoreactive .beta.-endorphin (IR .beta.EP) in cerebrospinal fluid (CSF) and blood plasma were investigated in conscious sheep in which the cisterna magna, a carotid artery, and a jugular vein were chronically cannulated. Serial samples of CSF and jugular venous blood were collected before and after acute arterial hemorrhage and in control experiments. Basal concentrations of IR .beta.EP were higher in plasma than in CSF. Plasma concentrations of cortisol and IR .beta.EP increased within 45 min of the commencement of hemorrhage and returned to near baseline levels within 2.25 h. The concentrations of cortisol and IR .beta.EP in plasma observed after hemorrhage were significantly different from those observed in controls (analysis of variance). Neither the molar nor the relative changes from initial concentrations of IR .beta.EP in CSF were significantly different between hemorrhage-stressed and controls by analysis of variance. These results show that hemorrhagic stress in conscious sheep elevates concentrations of IR .beta.EP in plasma but not in CSF, indicating that pituitary .beta.EP secreted into blood does not enter CSF in significant amounts.