Pancreatic endocrine cells in sea bass (Dicentrarchus labrax L.) II. Immunocytochemical study of insulin and somatostatin peptides.

Insulin (INS)- and somatostatin (SST)-immunoreactive cells were demonstrated by light immunocytochemistry in the endocrine pancreas of sea bass (Dicentrarchus labrax). INS-immunoreactive cells were identified using bovine/porcine, bonito, and salmon (s) INS antisera; the immunostaining was abolished when each antiserum was preabsorbed with its respective peptide but not with unrelated peptides. These cells also reacted with mammal (m) SST-28 (4-14) antiserum. The immunoreaction did not change when this antiserum was preabsorbed by bovine INS. INS-immunoreactive cells were located in the central part of the endocrine areas of the principal, intermediate, and small islets. Two SST-immunoreactive cell types (D1 and D2) were revealed. D1 cells, immunoreactive to SST 14 (562) and sSST-25 antisera, were located next to the glucagon-immunoreactive cells in the peripheral part of the endocrine areas. D2 cells, immunoreactive to SST-14 (562), SST-14 (566), and mSST-28 (4-14) antisera, were found in apposition to the INS-immunoreactive cells. The specificity controls showed that D1 cells expressed sSST-25-like peptides, while D2 cells might contain SST-14 and/or mSST-28-like peptides. The close topographic association between the different SST-immunoreactive cells and both glucagon- and insulin-immunoreactive cells might indicate the existence of a specific paracrine regulation of each endocrine cell type in the sea bass endocrine pancreas.