Immunohistological detection of leucine-enkephalin and influence of leucine-enkephalin on the nitric oxide synthase activity of the scallop Chlamys farreri

The study was designed to determine whether leucine-enkephalin (L-ENK) was present on the nerve cells of the scallop Chlamys farreri. Furthermore, the constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) activity was investigated after different doses of L-ENK were added into the haemolymph of C. farreri. Some nerve cells immunoreactive to anti-leucine-enkephalin sera were observed in the cerebral ganglia and pedal ganglia. Intracellular and extracellular cNOS and iNOS activity of the haemolymph was induced with increasing concentration of L-ENK. The highest of the extracellular iNOS and cNOS activity was 0.84 ± 0.02 (U) and 1.30 ± 0.07 (U), respectively. The highest of the intracellular iNOS and cNOS activity was 1.51 ± 0.13 (U) and 2.11 ± 0.13 (U), respectively. Both the intracellular and extracellular iNOS and cNOS activity was highest when the concentration of L-ENK was 5 µg mL^?1. Higher or lower concentrations of L-ENK did not significantly induce the cNOS and iNOS activity. The data suggests an involvement of opioid peptides in the regulation and improvement of the immune processes of C. farreri.