ACTA FAC. MED. NAISS. 2004; 21 (4):185-194

     Original article

Gordana Pešić¹, Zorica Jović¹, Karin Vasić¹, Snežana Cekić², Svetlana Antić³

¹ Department of Pharmacology and Toxicology, Medical Faculty, Niš
² Department of Physiology, Medical Faculty, Niš
³ Department of Anatomy, Medical Faculty, Niš

    SUMMARY

    The aim of this work was to clarify the role of opioid peptides, inhibitors of enkephalin degrading enzymes and releasing dipeptide on humoral immune response after intracerebroventricular (i.c.v.) application in rats.
    Methionine-enkephalin (Met-Enk) was i.c.v. injected through a permanently inserted cannula in various doses (0.01, 0.1, 1, 10, 20 and 50 mg/bw). Each rat received a total of 4 injections. Saline controls were treated in an identical manner. Met-Enk increased plaque forming cell assay (PFC response) in doses of 0.1 and 1.0 mg/bw, but in higher doses did not cause statistically significant suppression of PFC response. The immunopotentiating effects of Met-Enk were completely abolished by prior i.c.v. injection of ICI 174864 (delta opioid  antagonist) in doses of 10 and 50 mg/bw.
    The effects of Leucine-enkephalin (Leu-Enk) on PFC response were investigated by i.c.v. application of this peptide in doses of 0.1, 1, 10, 20 and 50 mg/bw. Treatments were performed in an identical manner as for Met-Enk. Leu-Enk caused statistically significant rise in PFC response when it was applied in doses of 0.1 and 1.0 mg/bw, whereas this substance in doses of 20 and 50 mg/bw exerted a suppression of the PFC response. The immunopotentiation, i.e. immunosupression was abolished by prior i.c.v. injection of -funaltrexamine (-FNA) - delta opioid antagonist (1.0 mg/bw of -FNA blocked the rise in PFC response caused by Leu-Enk, while 20 mg/bw of this antagonist blocked the suppression of PFC response caused by Leu-Enk).
    (Des-Tyr1)-Methionine enkephalin, inhibitor of endopeptidase and aminopeptidase, was i.c.v. applied in doses of 20 and 200 mg/bw. Each rat received a total of 5 injections. This inhibitor produced dose-dependent immunomodulation, i.e. in lower doses this substance induced rise in PFC response, whereas in higher doses suppression of immune response.
    Bestatin, inhibitor of aminopeptidase, i.c.v. injected in an identical manner as the previous inhibitor, produced a rise in immune response in dose of 20 mg/bw, but statistically significant depression of PFC response in dose of 200 mg/bw.
    N-carboxy-Phe-Leucine, a potent endopeptidase inhibitor, was i.c.v. injected in doses of 5 and 500 mg/bw. This substance caused dose-dependent immunomodulating effects: PFC response was potentiated when it was applied in a lower dose and suppressed in a higher dose.
    Actinonin, inhibitor of all enzymes that hydrolyse enkephalins, i.c.v. administered in doses of 20 and 200 mg/bw caused dose-dependent effects on humoral immune response. Actinonin produced the potentiation of PFC response in lower doses, whereas the suppression in higher doses.
    Kyotorphin, the "releasing" dipeptide, i.c.v. administered in the same way as previous inhibitors, induced immunopotentiation in dose of 5 mg/bw, whereas immunosuppression of PFC response in dose of 500 mg/bw.
    Naltrexone, the antagonist of opioid receptors, completely blocked the immunomodulating effects of (Des-Tyr)-Methionine enkephalin (naltrexone was applied i.c.v. prior to this inhibitor).
    These results suggest that opioid peptides, the inhibitors of opioid degrading enzymes and "releasing" dipeptide possess immunomodulatory activity. The immunological effects of Leu-Enk, enkephalinase-inhibitors and "releasing" dipeptide are dose-dependent phenomena.

    Key words: opioid peptides, inhibitors of opioid degrading enzymes, "releasing" dipeptid, humoral immune response.