Eine neue Methode zur Prüfung der Qualität von Nahrungsproteinen für den Erhaltungsstoffwechsel

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Abstract
The optimum amount of daily 15N-application and the optimum period for labeling adult rats was estimated in maintenance conditions with 15N ammonium acetate. Labeling periods of 7 and 10 days were combined with 10 or 30 mg 15N excess per day and 0.178 kg0.75. 15N-label in urine increased to a plateau within 3-4 days during 15N-feeding. After omitting 15N from the diet the 15N-label declined rapidly and became relatively stable within 3-4 days. The curve pattern for 15N-label in feces was similar, however, with a time lag of .apprx. 24 h. The ratio between 15N-label in urine and feces was constant from the 6th-10th day after the labeling period. This period should be used for the estimation of metabolic fecal N on the basis of 15N-label of N in feces and 15N-label of endogenous N secreted into the gastrointestinal tract. Both, 15N-label of urine and of TCA (trichloroacetic acid)-soluble fraction of plasma can be used as a indicator of the 15N-label of endogenous fecal N, but from a methodical point of view urine seems to be more convenient. Among the variants of labeling tested, the best was a 10-day period with 10 mg 15N''0.178 kg0.75 daily.