THE EFFECTS OF ETHANOL TREATMENT ON ENDOGENOUS OPIOID-PEPTIDES LEVEL AND ANALGESIA IN MONOARTHRITIC RATS

The effect of acute and repeated exposure to ethanol on endogeneous opioid peptides level in rats was studied. Acute ethanol administration decreased BETA-endorphin level in hypothalamus and anterior lobe of pituitary as well as alpha-neoendorphin in the spinal cord. In contrast, repeated ethanol treatment increased hypothalamic BETA-endorphin content and did not affect the peptide level in the pituitary. No changes in alpha-neoendorphin and dynorphin level after repeated ethanol administration were observed. Exposure of rats to long-term noxious stimuli by means of induction of monoarthritis prevented the increase in hypothalamic BETA-endorphin level by repeated ethanol treatment. As measured by tail-flick test only the first two administrations of ethanol resulted in analgesia. Further administration of increasing doses of ethanol did not affect the pain threshold. Altered response of endogenous opioid systems to repeated ethanol treatment as compared with effects of its acute administration may suggest involvement of these systems in development of tolerance to ethanol.