[Effect of glutamic acid content of the diet on the catabolic rate of isotope-labeled glutamic acid in rats. 3. Determination of 14CO2 and 15N excretion following intragastric infusion of 14C- and 15N-glutamic acid].

Male rats (body weight 100 g) received during a 8 days experimental feeding period diets with different contents in glutamic acid. The daily feed intake was restricted to the energy maintenance level of 460 kJ/kg0.75. The diet contained a mixture of L-amino acids corresponding to the pattern of egg protein except glutamic acid. Glutamic acid was added successively at 10 levels (0 to 14,8% of dry matter) and the resulting diets were fed to groups of 4 animals each. At the end of the experimental feeding period 14C- and 15N-labelled glutamic acid were applied by intragastric infusion. CO2- and 14CO2-excretion was measured during the following 4 hours and the urinary N- and 15N-excretion during the following 24 hours. The CO2-excretion decreased from 53 to 44 mmol CO2/100 g body weight with increasing levels of dietary glutamic acid. This change seems to result from the increasing proportion of amino acids as an energetic fuel. While the amount of oxidized glutamic acid increased with increasing supplements of glutamic acid the relative 14CO2-excretion decreased from 57 to 48% of the applied radioactivity. The urinary 15N-excretion during 24 hours was 31% of the given amount of 15N if no glutamic acid was included in the diet. This proportion increased successively up to 52% in the case of the highest supply of glutamic acid. Because the total N-excretion increased at the same extent as the 15N-excretion a complete mixing of the NH2-groups resulting from glutamic acid due to desamination with the ammonia pool was assumed. No correlation between glutamic acid content of the diet and specific radioactivity of CO2 or atom-% 15N excess of urinary N was observed.