beta-Endorphin regulates diverse functions of splenic phagocytes through different opioid receptors in freshwater fish Channa punctatus (Bloch): an in vitro study.

In this in vitro study, the role of beta-endorphin in the control of phagocytic and cytotoxic activities of fish splenic phagocytes was investigated. Further, the involvement of specific opioid receptor was explored. beta-Endorphin stimulated phagocytosis, whereas inhibited nitric oxide production as assessed by nitrite release. However, it had concentration-related biphasic effects on superoxide production, stimulatory at low and inhibitory at high concentration. Naltrexone, non-selective opioid receptor antagonist, antagonized the effect of beta-endorphin on phagocyte functions. Moreover, CTAP, selective mu-receptor antagonist, completely blocked the effect of beta-endorphin on phagocytosis and nitrite release. With regard to superoxide production, CTAP blocked the stimulatory effect of beta-endorphin at low concentration, while the inhibitory effect at high concentration was completely antagonized by selective delta-receptor antagonist, NTI. In conclusion, beta-endorphin acting via mu-receptor stimulated phagocytosis and inhibited nitric oxide production, while its biphasic effect on superoxide production seems to be mediated by mu- and delta-receptors.