Gastrointestinal Tract Metabolism in the Fetus and Neonate

Abstract

The transition from suckling to postweaned conditions in the developing rat provides a natural model for examining the effect of changes in energy requirements and oxidative substrates on intestinal metabolism. In the small intestine, oxidative substrates are not only delivered by the blood, but are immediately available from absorption of luminal substrates. Changes in the diet that occur during suckling and weaning have been shown to alter intracellular fatty acid concentrations in intestinal mucosal cells. The suckling rat pup diet consists of a high percentage of lipid (approximately 70% of total caloric content).1 During suckling, the concentration of free fatty acids in serum is markedly elevated as compared with the adult concentration2 and the intracellular concentrations of esterified fatty acids in jejunal mucosal cells are increased.3 During weaning the rat pup’s diet changes to one that is predominantly carbohydrate. Furthermore, the concentration of free fatty acids in the serum and the concentrations of esterified fatty acids in the mucosal cells decrease to those found in the adult. Finally, an increase in liver ketogenesis during the suckling period results in an increase in serum ketone concentrations. These abrupt changes in serum and intracellular concentrations of free and esterified fatty acids and ketone bodies provide a natural perturbation of substrates that can alter intestinal metabolism.