LEU-ENKEPHALIN ENHANCES INTERFERON SECRETION IN MICE

This work has explored the possibility that alterations of NK activity induced by the opioid pentapeptide leu-enkephalin (LENK) may reflect the alterations in secretion of IFN, an important regulator of NK acti vity. The NK activity in the spleen of mice was determined in parallel with the plasma IFN level 24 and 48 h after an i.p. injection of LENK (10 mg/kg). A known inducer of IFN secretion, polyinosinic-polycytidy lic acid (poly-IC), was also used. LENK injection significantly increa sed basal IFN secretion 24 and 48 h later. The level was comparable to that induced by poly-IC. However, LENK was not able to augment the po ly-IC-increased IFN level. The increase of IFN at 48 h coincided with a mild enhancement of NK activity in the spleens, but 24 h after LENK injection, the increased IFN level in plasma was associated with a sig nificant drop of splenic NK activity. LENK did not affect the NK activ ity stimulated with poly-IC. Naloxone (20 mg/kg), an opioid receptor-b locking agent, only partly diminished the LENK-induced IFN secretion. However, naloxone itself increased the plasma IFN level. These data in dicate that the immunomodulatory effects of the opioid peptide LENK in vivo are associated with alterations of IFN secretion.