Summary. The cellular composition and relative frequency of the occurrence of pancreatic endocrine cells were studied immunohistochemically in a primitive eutherian and arboreal folivore, the three-toed sloth, since previous histochemical and ultrastructural studies on the endocrine pancreas of the sloth have detected only a single islet cell type, the A cell.In the sloth pancreas, four types of endocrine cells immunoreactive for glucagon, insulin, somatostatin and serotonin (5-hydroxytriptamine)were found as reported in the pancreas of human and common experimental mammals, but pancreatic polypeptide-immunoreactive cells were not detected by either avian-or bovinepancreatic polypeptide antiserum.The endocrine cells were distributed mainly in the islets and partly also in the exocrine tissue including the pancreatic ducts. Larger or smaller clusters consisting of glucagon-and insulin-immunoreactive cells were also found frequently in the interlobular connective tissue. In the islets, glucagon-and insulin-immunoreactive cells were the most prominent cell type, while somatostatinand serotonin-immunoreactive cells were sparse. The most striking feature in the sloth pancreas is the high frequency of glucagon-immunoreactive cells, because these cells are by far less in number than insulinimmunoreactive cells in the islets of human and common experimental mammals. This appears to be an intriguing characteristic of the sloth pancreas in a possible relation to the animal's unique metabolic system and the phylogenetical position.The availability of specific antisera against the pancreatic regulatory peptides has made it possible to demonstrate immunohistochemically four different pancreatic endocrine cell types: glucagon (A), insulin (B), somatostatin (D) and pancreatic polypeptide (PP) cells. These four types of endocrine cells have been established as major pancreatic endocrine cells in higher vertebrates. Noteworthily, however, previous histochemical and ultrastructural studies on the pancreas of the three-toed sloth (Bradypus trydactylus) reported the presence of only a single islet cell type, the A cell (PINHEIRO et al., 1981;ABRAHAMSOHN et al., 1981). Although immunohistochemical studies have been carried out on pancreatic endocrine cells in a large number of mammalian species, no immunohistochemical studies have been available on this unique mammal, the sloth. Thus, the purpose of the present study is to determine, by immunohistochemical methods, the composition of the pancreatic endocrine cells in the three-toed sloth.
MATERIALS AND METHODSSix adults individuals of the three-toed sloth, Bradypus variegatus, 3 males and 3 females (3.2-4.5 kg body weight) were used in this study. They were captured under license in the forest near Recif e (Pernambuco, Brazil). The animals belonged to the same species as those used in previous studies by PINHEIRO et al. (1981) and ABRAHAMSOHN et al. (1981) and were identified as Bradypus tridactylus. Since it was confirmed that the South American three-toed sloth living in the fores...
