Modulation of humoral immune response by central administration of leucine-enkephalin: Effects of mu, delta and kappa opioid receptor antagonists

Abstract

The effect of leucine-enkephalin (Leu-Enk) on primary humoral immune response was investigated following intracerebroventricular (i.c.v.) administration of the peptide in-the rat. Leu-Enk stimulated plaque-forming 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 antagonist ICI 174 864 and kappa opioid receptor antagonist nor-binaltorphimine (nor-BNI) blocked stimulation and suppression of PFC response induced by Leu-Enk, respectively. The mu opioid receptor antagonist beta-funaltrexamine (beta-FNA) reversed both immunomodulatory effects produced 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 effects of Leu-Enk on PFC response were mediated by brain mu opioid receptors, and suggested a possible involvement of partial derivative and kappa opioid receptors.