Improved nitrogen metabolism in rats fed on lipid-rich liquid diets

N metabolism was studied in young rats fed on lipid-rich, isonitrogenous, purified liquid diets, a convenient and easy technique for inducing voluntary overfeeding of energy and lipids under controlled nutritional conditions. Overfed rats showed a marked N retention at the expense of a reduced production of urea. The capacities of isolated hepatocytes to synthesize urea and glucose from added precursors were greatly diminished. The activities of the urea cycle enzymes and several enzymes involved in the availability of NH3 for this pathway were concomitantly reduced in overfed animals. Therefore, our results showed an improved N metabolism in overfed rats promoted by the overfeeding of lipids that could be due to an enhanced biosynthetic utilization and a reduced catabolism of amino acids. In addition, the versatile and accurate technique for inducing overfeeding in young rats used in the present study could have many advantages for nutritional studies.