Seasonal Changes Of Internal Size, Intestinal Plasticity And Endocrine Cells In Bufo Raddei

Bufo raddei is a commonly observed amphibian, which mainly distributed innorthern China. In this paper, we measured the seasonal changes of many indices atdifferent levels (organism, organ, tissue, and biochemistry), including body mass,body length, internal organ mass, digestive organ length, small intestine histologicalparameters (diameter of transverse section, height of villus, thickness of muscularlayer, as well as long and short diameters of intestinal cells), activities of smallintestine digestive enzymes (amylase, protease and lipase), as well as morphologicalcharacteristics and distributive density of argyrophil cells and5-hydroxytryptamine(5-HT) cells of intestinal sections (duodenum, jejunum, ileum and rectum), by usingof morphological measurement, histology, Grimelius silver staining method,immunohistochemical techniques, and enzymatic method.The main results and conclusions are shown below:1. Body mass was significantly higher in female toads than in males, but not forcarcass wet and dry mass, as well as body length. These parameters above mentionedwere highest in autumn and lowest in winter. No sex differences were found ininternal organ wet and dry mass. Wet and dry mass in fat bodies and liver, as well astotal wet mass of digestive tract and digestive organs (except for oesophagus) showedthe highest in autumn or summer, lowest in winter. Wet and dry mass in ovary andoviduct was higher in winter or autumn than in spring and summer. No seasonaldifferences were found in wet and dry mass of testes. For other internal organ, nosexual and seasonal differences were found.2. No sexual variations were found in the total length of digestive tract, thelength of digestive organ, as well as histological parameters of small intestine. Thelength of oesophagus and rectum did not show significant seasonal changes. Insummer and autumn, the length of total digestive tract, stomach and small intestinewas significantly increased in comparation with winter and spring. No seasonalvariations were found in the thickness of muscular layer, and short diameter ofepithelium enterocytes, but diameter of cross section, height of villus, and height ofepithelial cells were increased in autumn or summer, decreased in winter or spring.The activities of amylase, protease and lipase in small intestine did not showsignificant sexual differences, but all displayed the highest in autumn, thensignificantly decreased in spring and winter. 3. Argyrophil cells distributed along the whole intestine of Bufo raddei indifferent seasons. In morphology, argyrophil cells were divided into two types: openand closed. Open type cells showed the pyramid, shuttle or long-bar in shape. Closedtype cells mainly displayed round or oval in shape. No sexual differences wereobserved for the distributive density of argyrophil cells along the different portions ofintestine. In summer and autumn, argyrophil cells showed the highest density in theduodenum, and the lowest in the rectum; Argyrophil cells showed the highest densityin the jejunum or duodenum and jejunum in winter and spring, respectively, and boththe lowest in the ileum. Distributive density of argyrophil cells in the duodenum,ileum and rectum was higher in summer and autumn than in winter; Distributivedensity of argyrophil cells in the jejunum was higher in spring and autumn than inwinter.4. Morphological characteristics of5-HT-producing cells along the intestine ofBufo raddei were similar to those of argyrophil cells. No sexual differences werefound for the distributive density of5-HT cells along the different portions of intestine.In summer and autumn,5-HT cells showed the highest density in the duodenum andjejunum, and the lowest in the rectum; In winter and spring,5-HT cells showed thehighest density in the duodenum, and the lowest in the ileum. Distributive density of5-HT cells in the duodenum was higher in summer, autumn and winter, and lower inspring; Distributive density of5-HT cells in the jejunum was higher in spring andautumn than in winter; Distributive density of5-HT cells in the ileum and rectum washigher in summer, and lower in winter and spring.Under the conditions of different seasonal environments, body mass, internal sizeand the mass and length of digestive organ in Bufo raddei was significantly increasedin autumn or summer, and declined in winter, which showed significant plasticitychanges. Such reversal changes may be related to food availability and unstabletemperature in different seasons. Further experimental evidences from histologicaland biochemistry levels demonstrate that the activities of amylase, protease and lipase,as well as histological parameters in small intestine combined with the variations fromorganic level, indicating the histological and biochemistrical mechanisms underlyingorganic level. No significant seasonal changes were observed for the morphologicalcharacteristics of both argyrophil and5-HT cells, but the distributive density showedplasticity changes with seasons, suggesting that this kind of toad may rely on thechanges of endocrine cell counts, not for the changes of morphological characteristics to regulate its digestive strategy and adapt to altered environmental conditions.