Effects of leucine-enkephalin on catalase activity and hydrogen peroxide levels in the haemolymph of the Pacific Oyster (Crassostrea gigas).

The nervous and immune systems of invertebrates can exchange information through neuropeptides. Furthermore, some opioid peptides can function as endogenous immune system messengers and participate in the regulation of the immune responses. The present study was designed to investigate the effects of leucine-enkephalin (L-ENK) on the activity of catalase (CAT) and hydrogen peroxide (H(2)O(2)) content in the haemolymph of the Pacific Oyster (Crassostrea gigas). The CAT activity and H(2)O(2) content were investigated after the haemolymph of the species was exposed to 1, 5, and 50 microg/mL of LENK. The results indicate that the intracellular and extracellular CAT activity was increased with increasing concentration of L-ENK, while the intracellular and extracellular H(2)O(2) content was decreased with increasing concentration of L-ENK. L-ENK may regulate the intracellular and extracellular CAT activity and H2O2 content via binding with opioid neuropeptide receptors on immunocytes of the oysters. The data strongly suggests an involvement of opioid peptides in the regulation of the antioxidant defence systems of Crassostrea gigas.