Induction of nitric oxide in vivo or in vitro by methionine-enkephalin

Opioid peptides are known modulators of immune functions. The aim of this study was to investigated the ability of methionin enkephalin (MENK)to induce in vivo or in vitro nitric oxide release from macrophages. We also investigated wether this effect was direct, opioid receptor mediated or indirect trough inductions of cytokines. The obtained results demonstrated that various concentration of MENK had no effect of nitric oxide release in vitro, while in vivo this effect can be stimulatory or suppressive depend of used dose. The stimulative, but not suppressive effect could be abrogated by naloxone.