[Time course of amino acid absorption in growing rats after feeding of a 15N-labeled wheat/yeast ration].

The time course of AA digestion, AA balance (sV AS), and AA absorption (wV AS) was estimated on growing rats (Wistar rats, LW = 124 g) in different sections of the intestinal tract using the combination of 15N tracer and TiO2 marker techniques. The animals received once a diet of 15N labelled wheat and yeast as protein sources supplemented by TiO2 as a marker. Up to 6 h after feeding the amino acid composition the 15N excess and the TiO2 content in the digesta of stomach, small and large intestine were determinated in the relation of amino acids resp. of 15N labelled amino acids to the marker. In addition the content of amino acids and the 15N excess of these amino acids were estimated in plasma. From these data the disappearance rates and the relation of exogenous to endogenous amino acids as well as the sV and the wV values of the different amino acids were calculated for the different gut sections. The following results were obtained: The relative disappearance rate for N and TiO2 marker out of the stomach went approximately parallel but with a delay for TiO2 of about 30 minutes. The AA composition of the stomach content, the small and the large intestine content did not vary in dependence of the time. The AA composition of the stomach digesta was nearly identical to that of the diet, while that of the small intestine was between exogenous AA composition (feed) and endogenous AA composition (digesta on protein free feeding). AA composition of the large intestine digesta showed quite big differences (bacterial AA break down and AA synthesis). Considering a delay time (small intestine: 1 h, large intestine: 4 h) the exogenous portion of the different AA remained constant in both of these intestinal sections during the whole experimental time. The exogenous AA part varied for small intestine digesta between 31 and 69% (mean value: 41%), and for large intestine digesta between 13 and 39% (mean value: 22%). The sV AS values in the small intestine (AA balance resp. precaecal digestibility) differed from 61% (threonine) to 86% (proline) with an average of 73.4 +/- 7.4%, those for wV AS (AA absorption) from 81% (lysine) to 94% (proline) with an average of 88.1 +/- 4.1%. There were significant differences between AA, but they are negligible for practical purposes.(ABSTRACT TRUNCATED AT 400 WORDS)