Enkephalins and immune inflammatory reactions.

Methionine-enkephalin (Met-Enk) and leucine-enkephalin (Leu-Enk) belong to family of opioid peptides. In vivo studies on immunomodulating activity of enkephalins performed in the rat revealed the following: (a) both neuropentapeptides showed a dual, dose-dependent effect, i.e., high doses suppressed while low doses potentiated immune responses; (b) Met-Enk is more potent immunomodulator than Leu-Enk; (c) high doses of Met-Enk suppressed immune inflammatory reactions, such as systemic anaphylactic shock, Arthus and delayed hypersensitivity skin reactions to protein antigen, allograft rejection, adjuvant arthritis, and experimental allergic encephalomyelitis. Met-Enk is more efficient when applied intracerebroventricularly. A preliminary clinical trial showed that intrathecally given Met-Enk exerted a beneficial effect on 13 patients with chronic severe progressive multiple sclerosis.