Changes in form and function of the gastrointestinal tract during starvation: From pythons to rats

Abstract

During episodes of food deprivation, animals enhance survival by minimising energy costs incurred by the metabolically demanding maintenance and activity of their digestive system. The response occurs at physiological, biochemical and molecular levels and mainly concerns the intestinal wall. After a feeding episode, this response leads to a rapid decrease in gut length and mass, as well as enzyme activities, protein synthesis and the expression of many proteolytic-related genes. Intestinal atrophy affects the mucosa, and induces a general decrease in its surface area through the diminishing of the mucosal area (shortening of the intestinal folds), changes in the microvilli surface area and by reducing both the size (hypotrophy) and number of cells along the intestinal barrier (hypoplasia). In most of the species studied, these morphological responses are time dependent and do not alter nutrient transport capacity, at least at the beginning of the fasting period. Fasting is usually anticipated in hibernating mammals, migratory vertebrates and infrequent feeders such as pythons. When preparing itself for fasting, the digestive system mainly uses tools such as hyperphagia, intracellular recycling and the production of new cells that are downregulated at the end of the postprandial period. As food deprivation continues starving animals may respond differently. This has been illustrated in rats that had reached a proteolytic phase during which energy requirements were mostly derived from increased protein utilisation. In these animals, cell proliferation and cell migration were seen to increase while apoptosis at the tip of the intestinal villi ceased. This has been considered as an optimising process that may also exist in other species.