Kappa-opioid receptor-mediated modulation of innate immune response by dynorphin in teleost Channa punctatus

The immunomodulatory role of endogenous opioid peptides released during stress has been extensively studied in mammals, but least explored in lower vertebrates. The present in vitro study for the first time reports the specific opioid receptor-mediated immunomodulatory role of dynorphin-A(1–17) in ectotherms. Dynorphin-A(1–17) had pleiotropic effects on phagocyte functions, stimulatory on phagocytosis and superoxide production while inhibitory on the nitrite release. However, the effect of dynorphin-A(1–17), whether stimulatory or inhibitory, markedly declined at high (10−5 M) concentration. Dynorphin-A(1–17) seems to mediate its action through opioid receptors since non-selective opioid receptor antagonist, naltrexone, completely blocked the effect of dynorphin-A(1–17) on phagocytosis, superoxide production and nitrite release. Moreover, among specific opioid receptors antagonists, only selective κ (kappa)-opioid receptor antagonist norbinaltorphimine was capable to antagonize the pleiotropic effects on phagocyte functions. The present study provides the direct evidence of immunomodulatory role of dynorphin-A(1–17) via κ-opioid receptor in freshwater teleost Channa punctatus.