[The secretion of radioactively labeled amino acids into the digestive tract. 3. 14C-labeling of the intestinal wall after subcutaneous injection of 14C-L-leucine in rats]

[N-metabolism as modelled by metabolism of 15N-labelled wheat in rat experiment]

Male albino rats of a weight of 90 g received a test ration with 15N-labelled wheat as protein source over a period of 1 to 8 days. The 15N-excess in urine, feces, some organs, the remaining carcass and in the blood was determined in dependence on time. On the basis of two different pool models the N-metabolism values could be calculated. Protein synthesis and disintegration rates calculated by means of the N- and 15N-balances of the pool in the steady state of the pool labelling amounted to 252.9 mg N per day resp 203.0 mg N per day. The calculation based on the time-dependent curve of the daily 15N-excretion in urine resulted in corresponding synthesis and disintegration rates of 197.0 mg N per day and 134.6 mg N per day. Labelling curve and results are discussed.

[Endogenous N-secretion in the small intestine of pigs]

The method of isotope dilution for the determination of endogenous N-secretion was used with three pigs of a live weight of between 15 and 27 kg, which were provided with simple cannulae at the end of the small intestines. The test animals received a single dose of a semi-synthetic ration with 15N-labelled dried curds as sole source of protein. The passage rate to the ileum ascertained with the help of 51Cr2O3 was 70% in 24 hours. During the test period of 24 hours the endogeneous N-amount in the ileum chyme was 1.11 g resp. 56.6 mg/kg live weight. Of that, 60% were allowed to be absorbed in the chyme at the end of the small intestine.

[New method of checking the quality of food proteins required for maintenance. 2. 15N excretion in feces of test rats labelled with 15N after feeding with different protein sources]

For 7 days 37 test rats received a casein diet with an extra of 6.6 mg 15N-excess in the form of ammonium acetate. From the eighth test day onwards 4 resp. 5 rats each received various protein sources under maintenance conditions (115 kcal/kg body mass0,75). The atom-% 15N-excess was determined in feces, blood liver and muscles (urine cf. 1st information). The endogenous quota of N in the feces was calculated as follows: (formula: see text). The numerical value of the TCA-soluble fraction of N in the total blood was corrected by the decrease of the atom-%15N' in the last 12 hours (time for the passage of the fecel matter from small intestines to excretion). Since the endogenously excreted N-amount varied greatly according to different feed, a scale is proposed as biologic value of food proteins, which exclusively refers to the metabolic fecal nitrogen (MFN) under conditions of maintenance (abbr. MFN-BV). A proposal for its definition is: (formula: see text). Above that, a total BV is suggested which also refers to maintenance metabolism. The total BV is calculated as follows: (formula: see text). The following values were ascertained for MFN-BV and total BV: casein = 80 and 82; complete egg=68 and 67; fish meal=61 and 86; Torula yeast=31 and 46; peas=41 and 43; soya (assay protein)=73 and 61; wheat=47 and 71; gelatin=64 and 42. Finally, the recommendation is given to include in feed tables real digestibility values for food proteins ascertained with the 15N method. In the above mentioned order the following values of the real digestibility of proteins were ascertained with the 15N method and classical methods: casein=98.2 and 97.2; complete egg=100.0 and 98.7; fish meal=96.9 and 93.4; Torula yeast=83.0 and 67.6; peas=97.1 and 85.6; soya (assay protein)=98.3 and 96.4; wheat=95.7 and 87.3; gelatin=99.1 and 96.0. *cf. 1st information Bergner et al. (1978)

[Nitrogen and amino acid resorption by swine. 4. Amino acid resorption]

The seeming and the actual absorption of amino acids of three pigs with a body mass of 50 kg was determined by inserting re-entrant cannulas at the upper small intestine and its end. The test ration contained dry curds labelled with 15N. The content of N and of amino acids as well as the 15N-excess in the amino acids were determined in the food and the chyme. This served the ascertainment of the actual absorption of amino acids in the small intestines.

[Nitrogen and amino acid absorption in swine. 3. Endogenous secretion and absorption of nitrogen]

The endogenous nitrogen in the duodenum and the distal segment of the small intestine of 3 fistulated pigs fed a 15-N-labelled feed protein was determined using the isotope dilution technique. Over 24 hours, the endogenous N secretion was found at least 12.5 g at the end of the duodenum. For the upper segment of the small intestine, a statistically secured correlation between endogenous nitrogen and chyme amount was found to exist. It was possible to determine the true and apparent absorption of the nitrogen for both individual segments of and the whole digestive tract.

[Secretion of radioactively labeled amino acids into the digestive tract. 4. 14C label and 14C-leucine in the digestive tract following subcutaneous injection of 14C-leucine in rats after ligation of the pancreas]

Secretion into the Gastro-Intestinal Tract of Amino Acids Labelled with Radioactive Isotopes. (4) 14C-Labelling and 14C-Leucine in the Gastro-Intestinal Tract after Subcutaneous Injection of 14C-Leucine to Rats with Tied-off Pancreatic Gland.