Effects of Leucine-enkephalin on Catalase Activity and Hydrogen Peroxide Levels in the Haemolymph of the Pacific Oyster (Crassostrea gigas)

Abstract: The nervous and immune systems of invertebrates can exchange informationthrough neuropeptides. Furthermore, some opioid peptides can function as endogenousimmune system messengers and participate in the regulation of the immune responses. Thepresent study was designed to investigate the effects of leucine-enkephalin (L-ENK) on theactivity of catalase (CAT) and hydrogen peroxide (H₂O₂) content in the haemolymph ofthe Pacific Oyster (Crassostrea gigas). The CAT activity and H₂O₂ content wereinvestigated after the haemolymph of the species was exposed to 1, 5, and 50 μg/mL of LENK.The results indicate that the intracellular and extracellular CAT activity wasincreased with increasing concentration of L-ENK, while the intracellular and extracellularH₂O₂ content was decreased with increasing concentration of L-ENK. L-ENK mayregulate the intracellular and extracellular CAT activity and H2O2 content via binding withopioid neuropeptide receptors on immunocytes of the oysters. The data strongly suggestsan involvement of opioid peptides in the regulation of the antioxidant defence systems ofCrassostrea gigas.