MODULATION OF HUMORAL IMMUNE-RESPONSE BY CENTRAL ADMINISTRATION OF LEUCINE-ENKEPHALIN - EFFECTS OF MU-OPIOID, DELTA-OPIOID AND KAPPA-OPIOIDRECEPTOR ANTAGONISTS

The effect of leucine-enkephalin (Leu-Enk) on primary humoral immune r esponse was investigated following intracerebroventricular (i.c.v.) ad ministration of the peptide in-the rat. Leu-Enk stimulated plaque-form ing cell (PFC) response in rats i.c.v. injected with 0.1 and 1 mu g/kg , whereas doses of 20 and 50 mu g/kg exerted immunosuppressive effects . I.c.v. treatment of rats with partial derivative opioid receptor ant agonist ICI 174 864 and kappa opioid receptor antagonist nor-binaltorp himine (nor-BNI) blocked stimulation and suppression of PFC response i nduced by Leu-Enk, respectively. The mu opioid receptor antagonist bet a-funaltrexamine (beta-FNA) reversed both immunomodulatory effects pro duced by Leu-Enk. Since beta-FNA alone had no effect on PFC response ( unlike ICI 174 864 and nor-BNI), these data showed that central effect s of Leu-Enk on PFC response were mediated by brain mu opioid receptor s, and suggested a possible involvement of partial derivative and kapp a opioid receptors.