The forestomach of rats and mice, an effective device supporting digestive metabolism in muridae (review)

Abstract

Summary The forestomach of rats and mice adapts the digestive regime of rats and mice from “food intake in bulks” to a “steady state digestion”. It stores well chewed and salivated food in amounts as needed for one to three hours or longer. The forestomach supplies its content for further digestion independently from its filling degree but in relation to the host's actual energy need during the light period or lipid metabolism during the dark period. Postprandial hyperglycemia and glycogen increase in the liver is lacking. Animals ingest most of their daily food during darkness. Meal frequency increases while the amount of food stored in the forestomach is hardly influenced. However, extremely high food demand or limitation of feeding time leads to increased filling per meal of the forestomach by four times and more, but in relation to “eating for calories”. The brain's appetite-regulating-network and signals which mechanically record the distension of the forestomach-stomach-cavity determine the ingested volume. In leptin-deficient Lep ob /Lep ob mice the filling volume of the forestomach per meal increases up to five times during the night and twice during the day. The frequency of meals declines. Emptying of the forestomach is controlled by a local feed back loop between duodenal reabsorption and the tension of the forestomach muscle fibres linked by humoral signals such as secretin and cholecystokinin. During storage in the forestomach food pap is subjected to digestion of starch, fat and chitin, but none of cellulose or protein can be observed. Microorganisms are without significance for the forestomach's function as shown in germ-free animals. Lactobacillae dominate in the variety of organisms lodged there. They are authochthonous and attached to the surface of the wall as dense carpets. Their lactic acid may have preservation effect on the food stored.