[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]

[Dynamics of amino acid and protein metabolism in laying hens after the administration of 15N-labeled wheat protein. 2. 15N excretion with nitrogen and basic amino acids of the feces]

Over 4 days 12 colostomized laying hens received together with a commercial ration labelled wheat with a 15N excess (15N') of 14.37 atom-%. The labelling of the basic amino acids amounted to 13.58 atom-% for lysine, to 14.38 atom-% for histidine and to 13.63 atom-% 15N' for arginine. 3 animals each were butchered 12 h, 36 h, 60 h and 108 h resp. after the last application of 15N. The heavy nitrogen in the total N and in the N fraction of non-protein origin as well as in the basic amino acids in faeces was daily determined for the individual hens in the total experimental period. On average the crude protein of faeces contained 5.45 % lysine, 2.32% histidine histidine and 3.68% arginine: the protein of faeces correspondingly contained 5.43% lysine, 2.32% histidine and 4.07% arginine. The quota of TCA soluble N in the total N of faeces amounts to one third on the 3rd und 4th days of the experiment and that of 15N' to 28%. The average atom-% 15N' of the protein fraction is 3.48 atom-% 15N' and that of the non-protein N fraction of faeces 2.93 atom-% 15N'. The apparent digestibility and that of the non-protein N fraction of faeces 2.93 atom-% 15N'. The apparent digestibility of the 14N of the ration on average amounts to 82.8% and that of the wheat 15N' to 87.5%. The average quota of the basic amino acids in the protein compounds of faeces amounts to 70.9% for lysine 15N', 73.7% for histidine 15N' and 70.3% for arginine 15N'. The digestibility of the 15N labelled amino acids amounts to 80.4% for lysine, 90.8% for histidine and 90.2% for arginine.

[Effect of graded dietary protein rations on the amino acid content of crude protein in various parts of the gastrointestinal tract and blood fractions of laying hens]

Four groups of four colostomized laying hens each received rations only consisting of wheat, vitamins plus a mineral mixture and a graded daily feed supply of 110 g, 88 g, 66 g and 44 g. The determination of amino acids from faeces was carried out after hydrolysis from a 6-day sampling period from the 16 laying hybrids. At the end of the experiment the animals were slaughtered. The corpuscular fractions of the blood, the contents of crop and stomach as well as of the intestines were also hydrolysed and the amino acid content in the crude protein was determined. In addition, the content of free amino acids in the blood plasma was determined. The content of amino acids in the protein of the corpuscular blood fractions remained uninfluenced by the decreasing amino acid and energy supply. The content of free basic amino acids in the blood plasma decreased with the decreasing supply with amino acids and energy, whereas the content of free amino acids with branched chains and hydroxylized ones increased. The content of glutamic acid in the contents of crop and stomach changed considerably in comparison with feed protein. The amino acid values of the crude protein in the contents of the intestines and in faeces to a large extent differ considerably from those of the wheat fed and are approximate values of body protein. Deficient supply with amino acids and energy did not influence the apparent digestibility of the amino acids.

[Nutritional physiology studies in pigs on the evaluation of modified proteins. 1. Results of the estimation of N-turnover, apparent and true digestibility of proteins in addition to apparent and true absorption of amino acids in the entire digestive tract]

Sulfuric acid-casein (A), spray dried isolated Vicia faba protein (B), Vicia faba protein/casein (1 : 1) protein fibres-untreated (C), treated with dialdehyde starch (D) or aluminum chloride (E) and meal of Vicia faba (F) were studied as sole protein sources in semisynthetic feed mixtures on 13 female pigs (40 to 45 kg body weight). Total utilization of nitrogen (b-value, PNu) and intermediate utilization (BW) were highest in A, followed by C. Protein C was superior to D. Protein E showed a drastic drop in protein quality compared with D because of a high decrease in S-containing amino acids content, however, their efficiency (bc-1-value) was not limited. Despite of a higher apparent digestibility by approximately 17 units in protein B, proteins B and F showed a similar quality. The true absorption of cystine (estimated by the balance of digestive tract) was corresponding to the protein quality of the respective step of treatment of protein C and was used for the correction of the gross content is S-containing amino acids.

[Absorption of 14C-leucine and 15N-leucine in rats after feeding a fish meal diet in comparison with a gelatin diet]

Albino rats received after nine days of adaptation to a fish meal diet in comparison with a gelatin diet 14C-U-Leucine and 15N-L-leucine via a pellet made from the specific diet after food deprivation for 15 h. Thereafter, the experimental animals consumed the non-labelled experimental diet ad libitum. Five times after the pellet intake, 30 min, and 1, 2, 4 and 6 h after injection of the labelled food, four experimental rats were sacrificed. The contents of the digestive tract and tissue samples were examined for 14C and 15N. We detected to following percentages of 14C-intake or the intake of 15N-excess (15N') in the TCA-soluble fraction of the gastric contents: [Formula: see text] We found in the TCA-soluble fraction of digesta of small intestine the following percentage of intake: [Formula see text] Where these values regarded as non-absorbed leucine, the 14C values obtained up to four hour period of experiment would be too high. Presumably, they are in the case of both diets simulated by other 14C-metabolites which originate from the leucine catabolism and reach the intestinal lumen. Amino acids labelled with 15N should be preferred in studies on the absorption of amino acids because, in case of catabolism, the 15N-aminogroup is excreted mainly in the form of urea via urine.

[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.

[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.

[Protein digestability and amino acid absorption in various segments of the digestive tract of pigs. 1. Methods of animal experimentation, protein content and amino acid patterns of the digesta in the small intestine and in feces after feeding different feeds]

Re-entrance cannulae were applied by way of operations at the end of the small intestine of a larger number of growing pigs. After a post-operative phase these animals were fed with various rations (N-free diet, fattening feed for pigs, rations with dried skim milk resp. wheat gluten + lysine and wheat + wheat gluten + lysine). During the main experiment periods the ileum digesta (24 hour-periods of collecting) and the feces were quantitatively registered. The protein and amino acid content ascertained in the feed rations, the digesta and feces samples are reported, comparatively evaluated and discussed. The amount of amino acids (in mg per kg intake of dry matter) contained in the ileum digesta after N-free feeding were statistically calculated with regard to differences occuring between the animals and days. For most amino acids a significant decrease in the ileum digesta could be detected during the course of the N-free feeding period. Moreover, the amount of amino acids in the ileum digesta was compared with the metabolic fecal amino acids, from which conclusions could be drawn concerning the disappearance rate of the individual amino acids in large intestine.

[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.

[Relationships between the apparent digestibility of crude protein and the amino acid balance of the swine digestive tract]

A diet of equal composition (88% barley, 5% extracted sunflower meal, 3% fishmeal and 3% yeast) was subjected to 9 different forms of thermal treatment and fed to experimental pigs. The biological value of the proteins was found to decline from 65.9 below 50. The amino acid balance of the digestive tract ("true digestibility of amino acids" according to other authors) proved to deteriorate due to the thermal treatment. The individual amino acids always revealed highly significant positive correlations with the apparent digestibility of crude protein. This finding is related with the often demonstrated fact that the fecal protein always has a constant amino acid composition, irrespective of feed protein and, consequently, only influences the quantitative fecal protein secretion, i. e. the amino acid balance of the digestive tract which is suggested to be the cause of the mathematical relations shown.

[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]

Experimental rats allotted in 4 different groups received 14C leucine injections at 4 different levels of specific 14C activity. Groups A and B were injected a leucine dosis corresponding to the daily requirement, the specific 14C activity being high (A) and low (B). Groups C and D were injected a leucine dosis of one ninth the amount applied to groups A and B, the level of 14C labelling being again high (C) and low (D). The 14C labelling of the TCE-soluble fraction of the 1st third section of the small intestinal wall in all 4 groups proved identical with the course of the curve representing the TCE-soluble fraction of the small intestine contents. The specific 14C leucine activity of the intestinal wall of the 1st third section of the small intestine was found to be 5 to 8 times lower than in the TCE-soluble fraction of the pancreatic gland. Thus a dilution effect has been produced from absorption. Two minutes after injection, the 14C labelling of the intestinal wall proteins had half the level of labelling of the pancreatic proteins. This finding applied to both the 1st and the 3rd sections of the small intestine. The results obtained allow to conclude that 14C labelling of intestinal wall proteins is relatively independent of 14C leucine absorption and is conditioned by the level of labelling of the plasma leucine.

[Some methodical problems in the determination of the true amino acid digestibility in swine]

Five castrated males bridge-fistulated at the end of the small intestine and fed a wheat-casein ration were used to study the influence of the microflora in the determination of the true amino acid digestibility applying the fecal analysis method. The experimental results allow to conclude that the influence of the microflora may be regarded as a very small one if certain parameters are taken into account in applying the fecal analysis methods.

[Secretion of radioactively labeled amino acids into the digestive tract. 2. 14C labeling and amount of 14C leucine in the intestinal contents after subcutaneous injection of 14C leucine in rats]

Experimental rats received a subcutaneous injection of 14C of varying activity. The rats were then killed in groups within a period of from 2 mins to 30 mins after the injection. A certain amount of 14C activity was detected in the intestinal contents as early as 2 mins after the injection, both as free 14C leucine and in the TCE soluble portion of the intestinal contents (TCE=trichloroacetic acid). A comparison of the degree of labelling in the TCE soluble and the TCE precipitable fractions of the intestinal contents showed that the most likely way for free 14C leucine to get into the lumen of the intestine is via the pancreatic juice while that for protein-bound 14C leucine is through the proteins in the pancreatic gland. The degree of labelling in both fractions decreased very steeply from the first to the third third of the intestine. This may be caused either by absorption of the secreted 14C leucine or may be brought about by a delay in food passage through the intestine.

[Secretion of radioactively labeled amino acids into the digestive tract. I. Report 14C labeling of the pancreas after subcutaneous injection of 14C-leucine in rats]

4 different groups of experimental animals (rats) were injected 14C leucine at 4 different levels of specific 14C activity. Groups A and B received a dosis of leucine corresponding to the daily leucine requirements of the animals. The specific 14C activity was high in group A and low in group B. Groups C and D were injected a leucine dosis at a level of 10% from the groups A and B. the specific 14C activity being again high (group C) or low (group D). The results showed that a true evalution of the experiment could lnly be achieved if the values were related to the true rate of labeling (DPM/mg N or specific 14C leucine activity). The "percentage of the injected dosis" proved to be unsuitable for the analysis of the experimental results when taken as reference frame. The levels of specific 14leucine activity in free plasma leucine were in the same order as the specific activities of the injected solutions (C greater than A greater than D greater than B) whereas the order of specific 14C leucine activities in the TCE-soluble fraction of the pancreatic gland (TCE-trichloroacetic acid) was found to be A greater than C greater than B greater than D. This was due to the higher rate of 14C-leucine transfer into the protein fraction in the animals of group C and D receiving a normal supply of leucine. In these groups an equilibrium in specific 14C-leucine activity between the TCE-soluble and TCE-precipitable fractions was achieved 20-30 mins after injection. A relatively high degree of labelling of the pancreatic protein was noted as early as about 2 minutes after the injection of 14C-leucine. This indicates that in studies on amino acid absorption the secretion of those amino acids that are first absorbed and then resecreted via the pancreatic gland should always be taken into account.

[Secretion of endogenous amino acids in the gastrointestinal tract and amino acid resorption in the swine]

A trial was performed with 2 fistula pigs (each with 2 fistulas, one located about 30 cm below the pyloric orifice and the other at the end of the small intestine). Animal A received a casein diet containing 14% crude protein for a period of 2 weeks before the tracer amino acid was administered. Animal B received the same diet for a period of 10 days and was then fed a diet (at the same protein level) containing gluten as sole protein source. The two tracer amino acids, 14C-U-L-leucine and 3H-4,5-(N)-L-lysine, were injected intravenously. The passage rates for dry matter, organic matter and N measured at the beginning of the small intestine were higher than the rate of intake. The rate of passage of amino acids was also found to be increased relative to the rate of intake. In general, this increase involved the non-essential amino acids to a much larger extent. A considerable proportion of the amino acids passing into the large intestine is not excreted with the faeces but is probably converted in catabolic processes. It is for this reason that any values for the efficiency of amino acid absorption calculated on the basis of data on the faecal excretion of amino acids will not provide conclusive evidence for the availability of dietary amino acids in processes of the intermediate metabolism. The rate of secretion of 3H and 14C radioactivity into the digesta of the small intestine was found to increase rapidly within 1-2 hrs after administration of the tracer amino acids. The 14C radioactivity detected was found to be almost exclusively derived from 14C leucine while only about 60% of the 3H activity found in the digesta of fistula I were shown to be bound to lysine. Labelled lysine and leucine (of endogenic origin) are absorbed into the small intestine at a slower rate (i.e. endogenic proteins are less efficiently digested) than the non-radioactive amino acids (of exogenic origin) so that a process of concentration of endogenic amino acids is observed towards the end of the small intestine.

[Resorption and incorporation of radioactive-labeled amino acids during administration of various protein carriers in rats. 3. Uptake of radioactivity by blood plasma, liver and muscular tissue and incorporation into tissue proteins after intragastric administration of 14C-leucine and 3H-glycine]

Growing male rats received diets of varying biological value (protein sources: powdered whole egg (V); fish meal (F); yeast (H); gelatine (G); protein-free diet (e)) for a 14-day feeding period. Subsequently, 14C leucine and 3H glycine were administered intragastrically. The level of uptake of 14C and 3H radioactivity into blood plasma, liver and muscular tissue and the rate of incorporation of the radioactive tracers into the proteins of these tissues was examined. A negative correlation was found to exist between the incorporation of radioactivity into liver proteins and the biological value of dietary proteins, the former being mainly dependent on the level of incorporation into the liver. For muscular proteins the rate of incorporation decreases with the decreasing biological value of the dietary proteins. This may be attributed to the fact that with poor protein nutrition the rate of protein synthesis in the skeletal muscles is also reduced. Comparative studies on the specific 14C radioactivity from free leucine made in the group on the protein-free diet and in the group receiving the whole egg diet showed that the leucine pool of the skeletal muscles was markedly redueced in animals fed a protein-deficient diet while the leucine pool in the liver remained comparatively constant.

[Resorption and incorporation of radioactive-labeled amino acids during the administration of various protein carriers in rats. 2. Uptake of radioactivity by tissues of the gastrointestinal tract after intragastric administration of 14C-L-U-leucine and 3H-glycine]

Male Albino rats (weighing 90-100 gms) were fed ad libitum for 14 days with limited periods of access to food. Powdered whole egg (V), fish meal (F), yeats (H), and gelatine (10% protein in dry matter) used as protein sources. Additionally, one group of rats received a protein-free (e). Radioactive tracers were administered by intragastric infusion of 25 mu Ci 3H glycine and 5 mu Ci 14C L-leucine per 100 gm of body weight 2 hrs after the feeding of 2 gm of the experimental diet per 100 gms of body weight. The level of uptake of radioactive tracers from the different sections of the gastro-intestinal tract was measurels of 3H and 14C labelling in intestinal tissues were observed 3 hrs and 7 hrs after infusion. The level of 14C labelling was found to be negatively correlated and the level of 3H labelling was positively correlated with the biological value of the diet. Intestinal tissues are capable of storing considerable amounts of 14C radioactivity. So, 72 hrs after infusion, the following levels of 14C radioactivity (expressed as percentage of the total dose of radioactivity) were found in tissues of the gastro-intestinal tract: whole egg: 8.4%, fish meal: 9.6%, yeast: 13.1%, gelatine: 14.9%; protein-free diet; 14.2%. The quotients correlating the levels of radioactivity from the intestinal contents with that found in the intestinal wall suggest that the walls of the small intestine possess a high capacity for absorption. At all times of radioactive measurements the walls of the small intestine were found to contain higher levels of both 14C and 3H radioactivity than the contents of small intestine.