Pancreatic endocrine cells in sea bass (Dicentrarchus labrax L.) I. Immunocytochemical characterization of glucagon- and PP-related peptides.

PP-, PYY-, and glucagon-immunoreactive cells were immunocytochemically identified in the pancreatic islets of Dicentrarchus labrax (sea bass). PYY cells also reacted with anti-PP serum. The specificity control showed that preabsorption of PP antiserum by PYY peptide abolished the immunostaining, while the reaction did not change when the PYY antiserum was preabsorbed by PP. These results suggested the existence of a PP/PYY molecule in the sea bass islets. The islet distribution of PP/PYY-immunoreactive cells differed markedly. Thus, in the principal islet and some intermediate islets few PP/PYY-immunoreactive cells are present (type I islets), whereas in the smaller and some intermediate ones they are numerous (type II islets). Adjacent sections stained by peroxidase-antiperoxidase (PAP) technique and individual sections stained by immunofluorescence double staining showed the coexistence of glucagon and PP/PYY-like immunoreactivities. Both islet types contained cells with PP/PYY coexisting with glucagon peptide, while cells showing solely glucagon immunoreactivity were found in type I islets only.