Immunohistochemical study of the six types of endocrine cells in the enteropancreatic system of the lizard Tropidurus torquatus (Squamata: Tropiduridae)

Abstract

The present study investigates the aspects of endocrine cells secreting cholecystokinin, gastrin, insulin, glucagon, somatostatin and serotonin in the enteropancreatic system of Tropidurus torquatus. The specimens were collected in Marambaia Island, Sepetiba Bay, Rio de Janeiro State, Brazil. The animals' intestine and pancreas were removed, fixed, processed and then subjected to immunohistochemical techniques. Three cell types, immunoreactive (IR) to gastrin, cholecystokinin-8 and serotonin, were identified in the intestinal mucosa. Serotonin was found in the small and large intestines, whereas gastrin and cholecystokinin-8 cells were only observed in the large intestine of T. torquatus. Glucagon, somatostatin and insulin were not observed in the intestines at all. Only glucagon, somatostatin and insulin were identified in the pancreas of the studied lizards. The dorsal lobe showed a large number of endocrine cells scattered throughout the exocrine parenchyma and in the exocrine duct walls. The present study shows that the intestine and pancreas of T. torquatus hold most of the regulatory peptides, presenting a structure similar to that in other vertebrates such as birds and mammals. The endocrine cells identified in the lizards' enteropancreatic system evidences the good phylogenetic preservation of the regulatory peptides' molecular structure.

An immunohistochemical study of endocrine cells in the digestive tract of Varanus salvator (Reptile: Varanidae)

“…The frequency of serotonin-IR cells in the large intestine was moderate compared to the caudal section of the small intestine. These results were similar to the serotonin-IR cells in the small and large intestine of Tropidurus torquatus [18] and in the gastric glands of mammals, including Manis javanica [13]. Serotonin-IR cells were detected in all parts of the digestive tract of Muntiacus muntjak with varied frequency [14].…”

“…A study on the distribution and frequency of endocrine cells in the digestive tract was focused on mammals such us Tragulus javanicus [ 11 ], Bubalus bubalis [ 22 ], Babyrousa babyrussa [ 12 ], Manis javanica [ 13 ], and Muntiacus muntjak [ 14 ]. Several studies that have reported on reptiles focused on small reptiles, including Tropidurus torquatus [ 18 ], Gekko japonicus , Eumeces chinensis , Sphenomorphus indicus , and Eumeces elegans [ 17 ].…”

“…Glucagon-IR cells in the digestive tract were found only in the stomach of the Gekko japonicus ; in the fundus, ileum, and rectum of the Eumeces chinensis ; in the ileum and rectum of the Sphenomorphus indicus ; but were not found in the Eumeces elegans [ 17 ]. Glucagon-IR cells also were not found in the intestine (small and large) of the Tropidurus torquatus [ 18 ].…”

“…Somatostatin-IR cells Available at www.veterinaryworld.org/Vol.13/September-2020/1.pdf were detected in the stomach and duodenum of Gekko japonicus, in the stomach of Sphenomorphus indicus and Eumeces elegans, and in all parts of the digestive tract of Eumeces chinensis [17]. Somatostatin-IR cells were not detected in the intestine (small and large) of Tropidurus torquatus [18].…”

“…Several animal studies on the distribution patterns of endocrine cells in the digestive tract were reported, including Tragulus javanicus [ 11 ], Babyrousa ­babyrussa [ 12 ], Manis javanica [ 13 ], Muntiacus muntjak [ 14 ], Rhinella icterica [ 15 ], and Hystrix javanica [ 16 ]. Regarding reptiles, almost all previous studies were reported on small reptiles such as Gekko japonicus , Eumeces chinensis , Sphenomorphus indicus , Eumeces elegans [ 17 ], and Tropidurus torquatus [ 18 ]. The patterns, activities, and dietary habits of mammals and reptiles are different and thus will affect the morphology and distribution of their endocrine cells in the digestive tract.…”