Digestible fiber (gum arabic), nitrogen excretion and urea recycling in rats

The effect of dietary fiber and level of amino acid (AA) intake on 1) partitioning of N excretion between urine and feces, 2) level of dietary AA on urea N kinetics, and 3) reutilization of urea-originated N into essential AAs was determined. In the first experiment, rats were adapted to one of two isocaloric (928-mJ.kg-1.day-1) and isonitrogenous (1.33-g N.kg-1.day-1) liquid diets containing 0 or 9% of nonprotein energy as gum arabic (GA) for 7 days. The rats were further subdivided, with half from each group continuing their diet and the AA intake of the remainder reduced by half (0.67 g N.kg-1.day-1). Daily N balance was determined over the next 5 days. For experiment 2, a catheter was inserted into the rats used for experiment 1, and 5-6 days later, urea production and urea N recycling were determined with [15N2]urea. In experiment 3, as in experiment 1, rats were adapted to the reduced AA diet with and without GA and then given [15N2]urea. Plasma lysine was then analyzed for 15N to determine whether AA synthesis by intestinal bacteria was a contributing source of AAs to the body and whether this process was increased with dietary fiber. Dietary fiber decreased urinary N excretion and increased fecal N excretion but had no net effect on N balance. On the adequate-AA diet, GA decreased urea production (523 +/- 36 vs. 374 +/- 47 mg N.rat-1.day-1, p < 0.01), and urea N recycling (47 +/- 4 vs. 30 +/- 6 mg N.rat-1.day-1, p < 0.01) was found.(ABSTRACT TRUNCATED AT 250 WORDS)