BIOCHEMICAL DETECTION AND IMMUNOHISTOCHEMICAL LOCALIZATION OF ENKEPHALIN-LIKE SUBSTANCES IN PERIPHERAL TISSUES OF THE SCALLOP PECTEN MAXIMUS (LINNAEUS)

This study focused on the biochemical detection of the methionine-enkephalin-, leucine-enkephalin-and methionine-enkephalin-arg-gly-leu-like peptides in the stomach, digestive gland, male and female gonads, muscle, gill and mantle of the scallop Pecten maximus using specific radioimmunoassays. Enkephalin-like substances were mainly present in the stomach and in the digestive gland, where leucine-enkephalin-and methionine-enkephalin-arg-gly-leu-like peptides were the predominant of these substances. In the gonads, muscle, gill and mantle, the enkephalin-like contents were close to the sensitivity threshold of the enkephalin antibodies. The enkephalin-like contents measured in September, in the digestive complex, were significantly higher than in December, when the bivalves have undergone a period of starvation. Immunohistochemical assays were performed on the stomach and the digestive gland to localize the enkephalin-like materials. In these organs, which are the main sites of the digestive process in Bivalyia, the enkephalin-like materials were mainly confined to the endocrine-like cells. These results suggest that in Pecten maximus, opioids may be involved in the digestive processes mainly through enkephalin-endocrine-like cells.