Das Kompartment-Modell — eine Methode zur Bestimmung resorptionskinetischer Kenndaten von Aminosäuren

Quantification of lysine dynamics in the Japanese quail

To cockerels of the Japanese quail four graduated flooding doses of 14C-labelled L-lysine (20-160 mg) in starch gel were administered into the crop. The animals were slaughtered between 40 and 210 min thereafter. The TCA soluble fraction of the gastrointestinal tract, of blood plasma, liver and muscle were analyzed for their lysine content and its specific radioactivity. Incorporation of radioactivity into the TCA insoluble fraction of the same organs was also followed. After quantification of lysine losses by catabolism and excretion a multicompartment model of lysine dynamics in the quail was set up. Model parameter values in general agree with independently obtained data. The necessity of model validation and extension as well as possibilities for model applications are pointed out.

[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.

[Investigations of the metabolism of colostomised laying hens with 15N-labelled wheat. 5. Incorporation and distribution of 15N in the contents of the intestinal tract, the tissue of stomachs and the segments of the intestines]

In an experiement with 3 colostomised laying hybrids each animal received 80 g pelleted mixed feed and 40 g 15N-labelled wheat with 20.13 atom-% 15N-excess (15N') over a period of four days. On the following four days the hens received rations composed in the same way with uulabelled wheat, however. Of the individual tissues and organs extracted from the slaughtered hens 15N' was determined in the total N and the amino acids lysine, histidine and arginine in the individual segments both of the gasto-intestinal tract and in its contents. On a average, the amount of 15N' in the stomachs, the small intestines and the colon was 43.7%, 27.2% and 29.1%. The tissue of the small intestines contained, on an average, the highest 15N' in lysine of all the basic amino acids. It amounts to 0.82 atom-% 15N' for lysine, O.55% for histidine and 0.63 atom-% 15N' for arginine. On an average, the percentage of the 15N' of the basic amino acids from the corresponding total 15N'-amount of the charges is in the contents of the gasto-intestinal tract 20.5%, in the stomach tissue 28.0% and in the tissue of the small intestines 24.4%, of the caecum 21.5% and of the rectum 25.7%.

[Protein digestibility and amino acid absorption in various segments of the digestive tract of pigs. 5. Results of the application of 35S-methionine]

The intake, excretion and the rate of flow of protein, methionine and 35S were measured at four pigs (live weight 63 kg) with re-entrant cannulae in the duodenum and the ileocecal region after the oral application of 35S-methionine and the feeding with a wheat + wheat gluten + lysine resp. a protein-free diet over a period of 7 days. From the measured values one pattern each for the N- and the methionine metabolism was laid down with the help of the compartment model, and the endogenous and exogenous levels of protein resp. methionine in the duodenum, the ileum and in feces were estimated.

[Studies on nitrogen and amino-acid absorption in the swine. Part 2. The course of 15 N labeling in the chyme, urine and blood]

Three female pigs provided with re-entrant canulas at the beginning and the end of the small intestine and catheterized for blood and urine collection were once fed a 15N-labelled mixed diet. Until 48 hours after feed intake chyme from the canulas and urine and blood were collected at varying intervals. All 15N-frequencies measured in the duodenal chyme were found to be below the labelling of the feed protein. Until 11 hours after intake of the labelled feed, the residue obtained by centrifugation of the intestinal contents revealed the highest 15N-labelling. Only slight differences were found in the frequencies of the other fractions (proteins, peptides, free amino acids). The almost constant labelling of all fractions in that period is indicative of a dilution with endogenous nitrogen being constant in comparison with food N. The 15N-frequencies of the chyme fractions observed at the end of the small intestine allowed to conclude that the breakdown of the food proteins is more complete than the disintegration of the endogenous proteins.

[Nitrogen metabolism of broilers fed 15-N labeled wheat. 4. 15-N concentration in muscles and nitrogen utilization]

Broilers were fed 15N labelled wheat and the concentration of the labelled isotope in muscular tissue was determined. A negative correlation was found to exist between the percentage proportion of N in the muscle fractions and the level of 15N frequency established 12 hrs after administration of the labelled ration. Higher rates of tracer incorporation were observed in the muscles of legs and other muscles (predominatly red muscles) than in pectoral muscles (white muscles). The heart was shown to exhibit the lowest N content and the highest level of 15N frequency of all muscle fractions. In view of the fact that some specific difficulties will arise when certain factors (trace elements, vitamins, ergotropic substances, genetic factors) which influence the N metabolism of fattening poultry, are estimated on the basis of the conventional N balance trials the present tracer technique is recommended for use as an alternative method in studies of the kind just described. In the present trial 20% of the wheat N were utilized for the production of meat N in muscular tissue.

[Nitrogen metabolism of broilers fed N-15 labeled wheat. 3. Blood, liver, spleen, thymus, kidney, brain, pancreas, labile N reservoir]

Studies on the N metabolism of 4-week-old male broilers fed 15N Labelled wheat revealed a close correlation existing between the levels of 15N concentrations in the small intestine and in the plasma NPN fraction of the blood. The highest level of excess 15Natom0/0 in plasma proteins was noted as late as 20-30 hrs after administration of the last tracer dose. The mean life time of plasma proteins in broilers is less than 2.0 days. The rapid and statistically significant decrease of 15N frequency in the liver, spleen, thymus, and kidneys in the period from 12 hrs after withdrawal of the last 15N dose until the end of the trial reflects the intensity of N turnover in these organs. In the period from 6 hrs to 12 hrs after the last N intake the mean quantities of N in the liver, small intestine and kidneys decreased by 18%, 29%, 26% and 16%. The quantity of N accumulated in these organs after food intake is gradually released into the organism.

[The nitrogen metabolism of broiler chickens with 15N-labeled wheat. 2. Report. 15N concentration in the gastrointestinal tract and its contents]

17 broilers received a wheat-soya bean meal-pea nut ration containing an excess of 15N atom% (6.54%). The birds were slaughtered 3, 6, 12, 36, 60 and 108 hours after the last 15N'-intake. Up to 12 hrs after slaughtering the contents of the crop and the stomachs were found to contain a higher excess of 15N atom% than the food. The contents of the small intestine at that time contained only 1/4 of the 15N concentration present in the crop and the stomachs (2.7%). Later on the excess of 15N atom% decreased to 1.7%, 1.4% and 0.8% and was 4 times as high as that found in the crop and the stomach. Higher 15N' concentrations, compared with those in the small intestine, were found in the contents of the caecum, the colon, and the rectum, for a period of up to 12 hrs after administration of the last portion of labelled food. The 15N' concentrations in the crop and the stomachs are due to a more prolonged storage of wheat relative to that of the extracted meals. The interrelationship between the contents of the small intestine and the contents of the higher sections of the gastro-intestinal tract suggests that a secretion of N-containing substances takes place, although it was not possible to determine these substances quantitatively. Values for the excess of 15N atom% in the crop and oesophagus and in the muscular stomach were found to be in close correspondence both with regard to their level and time pattern. The decline in the glandular stomach was more rapid than in the muscular stomach. A very close correlation (r=0.99) was found between the 15N atom% in the contents of the intestine and in the intestinal wall. The N content of the small intestine (expressed as mg) was significantly higher after 3 hrs and 6 hrs of fasting than after a fasting period of 12 hours. Theoretical aspects of the involvement of the intestine in the process of metabolism are discussed in some detail.

[Problem of nitrogen metabolism in monogastric animals]

A new method has been developed for determining the proportion of endogenic and exogenic faecal N by measuring the degree of specific labelling in the feeding-stuff (administered orally) and in the excreta (faeces and urine). The method has also been developed to find out whether the endogenic excretion of intestinal N is actually independent of the N intake. The present technique had been worked out on the basis of the model that had been originally established by Czarnetzki et al. in 1969 with the aim of characterizing processes of nitrogen metabolism in monogastric animals. As a result, a multi-compartment model was developed and a number of conclusions were derived from it. These conclusions were tested in 3 series of experiments on rats fed 15N labelled spring barley and 15N labelled feed yeast. Additionally, 15N labelled experimental rats were used receiving unlabelled extracted soya bean meal. The proportion of endogenic intestinal nitrogen (DVN) varied between 15-22% relative to the proportion of N ingested. The relative proportion of endogenic faecal N in the tota faecal N was found to be 100% in the case of the nitrogen-free diet. With increasing levels of dietary N this proportion lended to decrease down to a final value that was quite characteristic for each partitular feeding-stuff. The absolute amount of endogenic faecal N, however, was found to increase with increasing N levels. This shows that contrary to current views, DVN is not constant and is not independent of protein intake. Rather, a close relationship was found to exist between the level of N intake and DVN excretion (r = 0.951...0.972). So, the proportion of exogenic N contained in the faeces is much smaller than was previously assumed on the basis of the classical and regressive methods. These were based on the assumption that DVN is constant. Consequently, higher digestibility values will be obtained in comparison with those calculated on the basis of the previous methods. Digestibility data for spring barley increased from 83.9 to 95.6, i.e. by 11 digestibility units; for feed yeast there was an increase by 6.2 units, from 83.3 to 90.0; and for extracted soya bean meal an increase of 6.2 units was observed (from 90.7 to 96.9).

[Resorption and incorporation of radioactive labeled amino acids during administration of various protein carriers in rats. 1. Resorption of 14C leucine and 3H glycine after intragastric administration]

Male Albino rats (90-100 g) were fed ad libitum (with limited periods of feeding) for 14 days. The diets were adjusted to a crude protein content of 10%. Powdered whole egg, fish meal, yeast and gelatine were used as protein sources. Additionally, one group of rats was fed a protein-free diet. On the 15th day of experiment the rats were fed a test diet at a level of 2 g per 100 g of body weight. 2 hrs after that the rats received 25 muCi of 3H glycine and 5 muCi of 14C-L-Leucine per 100 g of body weight administered by way of intragastric infusion. It was found that a large proportion of the radioactive amino acids were absorbed as early as after 0.5 hr. The highest rate of absorption was observed in animals fed dietary proteins of poor quality or a protein free diet, so that in animals receiving a gelatine diet or a protein-free diet only 68.4% or 56.4% of the administered amount of 14C activity were detected inside the gastro intestinal tract after 0.5 hr. Analogous data for the 3H activity were 52.4% and 25.3%. Maximum absorption occurred after 3-7 hrs. Following this the level of radioactivity in the intestinal contents again increased reaching a peak value after 14-24 hrs; in the case of 14C activity this peak value amounted to 25.4% of the administered dose in animals fed the gelatine diet and 32.8% in the group receiving the protein-free diet. It was established that the major proportion of the resecreted amount of 14C activity was present in leucine. Until 72 hrs after the intake of 14C activity the level of radioactivity was again found to decline, a processes which was induced by processes occurring in the large intestines. Moreover, evidence was obtained in confirmation of previous findings, indicating that the composition of faecal amino acids was constant and unaffected by dietary proteins.