STARCK, J.M.; ABE, A.S.; NETO, A.C.; University of Jena, Germany; UNESP Rio Claro, Brazil: Morphological and Physiological Responses of the Digestive Tract to Feeding in Caimans

Broad-nosed caimans (Caiman latirostris) experience considerable fluctuations in food supply. We asked: (1) what happens to the gastrointestinal tract when caimans are fasting, i.e., when the intestine is non-functional; (2) is metabolic rate up-regulated during digestion? We used ultrasonography and histological techniques to study structural changes of the GI-tract in response to feeding and fasting. We measured oxygen-consumption in a closed system before and after feeding. Twenty animals were randomly assigned to 2 groups, feeding and fasting. Fasting animals were fasted for 6 weeks before the experiment. The feeding group was offered food every third day. When fasting animals were fed, the size of duodenum, small intestine, and liver increased significantly within 2 days. Ten days after feeding, organ size was again downregulated to fasting size. Fasting of previously feeding individuals resulted in declining organ size. Up- and down-regulation could be elicited repeatedly. Histology revealed that intestinal villi of the duodenum and the small intestine increased in length. We observed incorporation of lipid droplets into enterocytes. There was no cell-production associated with increase in organ size. Instead, the mucosa epithelium changed its configuration from pseudostratified during fasting to single layered when digesting. Associated with an increase in organ size we observed a significant increase of resting metabolic rate. The morphological and physiological responses to feeding of caimans are identical with those in Python molurus and Thamnophis sirtalis. This suggests that rapid, repeated, and reversible up- and down-regulation of organ size and function is a shared character of snakes and crocodilians (DFG grant STA 345/8-1 to JMS).