An immunohistochemical study of enteropancreatic endocrine cells in larvae and juveniles of the southern-hemisphere lampreys Geotria australis and Mordacia mordax.

The cell types within the endocrine pancreatic tissue and anterior intestine of larvae and juveniles of representatives of the two southern-hemisphere families (Mordaciidae and Geotriidae) were compared, using immunohistochemistry and antisera against insulin (lamprey, bovine), two somatostatins (SST-14, -34), two PP-family peptides (aPY, NPY), and salmon glucagon and glucagon-like peptide (GLP). Cells of the islets and some anterior intestinal cells in larval Mordacia mordax showed intense immunoreactivity (IR) to the two insulin antisera. In contrast, immunoreactivity to these antisera in the islets of larval Geotria australis was restricted to antibovine insulin and even then the staining was weak. The islet cells did not IR with other antisera, but IR to aPY and NPY antisera was noted in a few intestinal cells of both species and cells in the intestine of G. australis were positively stained with antiSST-14 and/or -34. The single islet organ of adults of both species consisted only of antiinsulin-IR, B cells, and D cells, which were IR with only antiSST-14. Although IR was not seen in islet tissue to antisera against aPY, NPY, glucagon, and GLP, four cell types were identified in the intestinal epithelium in both species based on their IR to these antisera and the two antiSSTs. A fifth cell type IR to the two insulin antisera was recognized in adult M. mordax. The types and IR of endocrine cells in the enteropancreatic system of two southern-hemisphere lamprey families are compared with those of the Petromyzontidae, the single family of holarctic lampreys. Differences are discussed in relation to variations in hormone processing and whether they are a consequence of varied ontogenic and phylogenetic history among the extant Petromyzontiformes.