Anatomia microscópica do pâncreas e detecção de células neuroendócrinas imunorreativas a insulina, glucagon, somatostatina, serotonina e polipeptídeo pancreático de Phrynops geoffroanus (Schweigger, 1812) e Hydromedusa maximiliani (Mikan, 1820) (Testudines, Chelidae)

Abstract

Comprehension of the physiological processes of vertebrates is essential to obtain data on the biology of the various species. The pancreas is a mixed gland that in involved in digestive and homeostatic processes. Understanding the morphology and physiology of the pancreas in all classes of vertebrates is fundamental to clarify this gland's function in the digestion of foods, to help shed light on nutritional factors that can improve the management and conditioning of species in their ecosystems. In the case of Brazilian species, this attention is particularly important, since many are classified as vulnerable by the IUCN (2017) due to anthropic alterations of their natural habitats. This article describes the histology and immunohistochemistry of the pancreas of two species of the Chelidae family. For this purpose, the pancreas of four specimens of Phrynops geoffroanus and four of Hydromedusa maximiliani that had been fixed in 10% formol and deposited in the collection of Juiz de Fora Federal University were routinely processed for histology to obtain sections with thickness of 5 μm. The histology of the pancreas of P. geoffroanus and H. maximiliani is characterized by an endocrine portion dispersed among the pancreatic acini, forming or not forming endocrine groups similar to pancreatic islets. No connective tissue capsule is observed separating the pancreatic islets from the surrounding exocrine portion. The immunohistochemical analysis revealed four types of endocrine cells in P. geoffroanus: cells producing insulin, glucagon, somatostatin and pancreatic polypeptide. In H. maximiliani, only three cell types were found, producing insulin, glucagon and somatostatin. The cellular organization of the endocrine groups similar to pancreatic islets is different in the two species. In P. geoffroanus, the insulin-producing cells are positioned in the center, while those producing glucagon occupy the periphery. In turn, in H. maximiliani, these to cell types are interspersed, generally around the blood vessels. These observations will help understand the digestive physiology of the two species and provide data for comparative analyses with other freshwater turtles