Effect of hypoglycemic stress on plasma and cerebrospinal fluid immunoreactive beta-endorphin in conscious sheep

The effect of insulin-induced hypoglycemic stress on the concentrations of immunoreactive beta-endorphin (ir beta-EP) in plasma and cerebrospinal fluid (CSF) was examined in conscious non-pregnant ewes in which the cisterna magna and a jugular vein had been previously catheterized. In control experiments, no significant changes were observed in plasma cortisol or ir beta-EP and CSF ir beta-EP concentrations. During hypoglycemia induced by intravenous injection of 20 units of insulin, plasma cortisol concentrations rose significantly, reaching a peak 1.5 h after injection. The changes in plasma ir beta-EP concentration were significantly different between hypoglycemic and normoglycemic sheep (analysis of variance, P = 0.0089). Following insulin injection, mean plasma ir beta-EP rose by 100% within 0.75 h, continued to rise six-fold over initial concentrations by 2.25 h, and remained elevated for 3.75 h. The CSF ir beta-EP concentrations following insulin injection were not significantly different from those observed in controls. These results suggest that if beta-endorphin mediated hypoglycemic stress-induced analgesia, its actions may be peripheral, not central.