Lipopolysaccharide increases endogenous morphine levels in rat brain.

The present study was designed to determine whether whole body injection of lipopolysaccharide increases endogenous rat brain morphine levels. High performance liquid chromatography coupled to electrochemical detection and gas-chromatography mass spectrometry reveal that the resting brain morphine level is 7.0+/-3.2ng/g wet weight. In a time dependent manner, intraperitoneal injection of lipopolysaccharide (10 microg), leads to an increase of brain morphine level with a peak reaching after 36h post injection. After 72h following the lipopolysaccharide-injection, morphine levels increased to 66.0+/-5.4ng/g brain wet weight (P<0.001). Furthermore, 96h of fasting also increased the brain morphine level to 44.0+/-3. 6ng/g of brain wet weight. These results suggest that rat brain morphinergic processes respond to organismic challenges after a significant latent period.