Adaptive changes of gastro-entero-pancreatic system endocrine cells in the black-spotted pond frog Rana nigromaculata after fasting

Abstract

Abstract Changes in distribution density, morphology and secretory content of endocrine cells in the gastro- entero-pancreatic system of black-spotted frogs Rana nigromaculata before and after fasting were investigated using immunohistochemistry and antisera to six gut hormones. Six types of endocrine cells were detected in the digestive tract of Rana nigromaculata, including 5-hydroxytryptamine (5-HT), gastrin (GAS), somatostatin (SOM), glucagon (GLU), pancreatic polypeptide (PP) and vasoactive intestinal polypeptide (VIP) cells. After fasting, the density of 5-HT cells in the esophagus, cardia and fundus, GAS cells in the fundus and pylorus, PP cells in the fundus decreased significantly (P < 0.01), while SOM cells in the cardia, GLU cells in the rectum increased significantly (P < 0.01). The cytoplasmic processes of 5-HT cells became shorter or not detectable. The secretory content of GAS cells reduced in the cardia. The positive immunostaining reaction in the perinuclear region of SOM cells in the cardia, fundus and pylorus became weaker, while the staining intensity in the periphery of these cells became stronger. VIP cells were not detectable in the whole digestive tract after fasting. Five types of endocrine cells were found in the pancreas of Rana nigromaculata, including 5-HT, GAS, SOM, GLU and PP cells. After fasting, the density of 5-HT cells decreased slightly (P > 0.05), while SOM, GAS, GLU and PP cells increased significantly (P < 0.01). Furthermore, the secretory content of GLU cells increased significantly. Considering their functionalities, our results indicate that the changes of GEP endocrine cells in Rana nigromaculata responded adaptively to starvation-induced stress.