Simon O

Einfluß des Gehaltes nativer Rohfaser in Diäten von Ratten auf die Aminosäurenresorption

Growing rats received either a protein-free experimental diet or a diet containing 15% crude protein (whole egg). The crude fibre content of the diet was adjusted to 5%, 10%, or 20% by adding various proportions of what straw meal. Following a preliminary 7-day period of feeding the animals received L-14C-Leucine administered by stomach tube or by subcutaneous injection. In a 72-hour post-experimental period analyses were made to investigate the urinary and faecal excretion of radioactivity. About 50% of the amount of radioactivity excreted with the feaces were of endogenic origin. In general, higher percentages of straw meal in the diet produced higher levels of faecal 14C excretion. It was only in the animals placed on the whole egg diet that the TCA soluble portion of radioactivity was found to rise with the increasing straw content of the diet. The experimental results substantiate the assumption that native crude fibre influences the process of intestinal sloughing and, additionally, it is capable of abosrbing or adsorbing amino acids, peptides or protein, due to its spatial configuration. Similarly, it affects the digestion and resorption of proteins.

Untersuchungen zur Sezernierung endogener Aminosäuren in den Verdauungstrakt und zur Aminosäurenresorption beim Schwein

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.

Studies on the secretion of amino acids and of urea into the gastro intestinal tract of pigs

Three pigs, of 34 kg live weight, were each fitted with re-entrant cannulas both in the duodenum and terminal ileum and catheters in the jugular vein and in the carotid artery. Pigs received a diet based on wheat and dried skimmed milk in equal amounts at 12 h intervals. During the preliminary period the digesta flowing from both duodenal and ileal cannulas were collected over 12 h after feeding on two consecutive days and half of them were reintroduced into the gut and half were stored at -20 degrees C. During the experimental period 15N-urea was infused into the jugular vein for 12 hours starting with the morning meal. Total amount of urea infused was 5 g containing 1.22 g 15N-excess. The digesta from both proximal duodenal and ileal cannulas were collected and stored, while the digesta from the preliminary period were reintroduced into the respective distal cannulas. Blood samples were taken at different time of infusion. At the end of infusion period the animals were sacrificed and samples of the contents of the digestive tract and tissues were taken. Urea flux calculated according to atom-% 15N-excess of urea N in plasma was 1.23 to 2.37 g/kg body weight/day. In the duodenal digesta 94.5 +/- 0.2 and in ileal digesta 57.1 +/- 7.39 per cent of 15N were in the TCA soluble fraction. The total amount of 15N in the duodenal digesta was 1.7 to 6.3 times greater than in the ileal digesta. Only small amount of 15N was found in the caecum and almost none in the contents of colon and rectum. It is concluded that urea is secreted into all parts of the digestive tract, the main sites of urea secretion being pancreatic juice and/or bile as well as the small intestine. The total amount of urea secreted is assumed to be similar to the daily urea excretion.Three pigs of 34 kg live weight were fitted with a re-entrant cannula in the duodenum, and with two catheters placed in the jugular vein and carotid artery. They were fed 1.2 kg/d of wheat-dried-skimmed milk diet. Digesta from the proximal duodenal cannula were collected for 12 h on 2 consecutive days; 50% were reintroduced into the respective distal cannula and 50% were stored at -20 degrees C. Three days later 14C-leucine was infused into the jugular vein for 12 h, starting with the morning meal. During this period the digesta from the proximal cannula were collected and stored for analysis while the digesta collected previously were reintroduced into the distal cannula. Blood samples were taken from the carotid artery. The total flow of duodenal digesta in 12 h was 5760 +/- 530 g. On average 70 percent of the radioactivity in digesta was associated with the TCA-precipitable fraction. During hours 0-3 and 11-12 of infusion 60-70% and 96-98% of the radioactivity in the TCA precipitable fractions was in leucine. In the TCA soluble fraction only 30-40 per cent of the radioactivity was associated with leucine. At the plateau 2.1 and 3.3% of infused 14C-leucine and of radioactivity were recovered in the duodenal digesta. The calculated amount of endogenous protein passing the duodenum was 20.4 g/d/pig. The results are discussed in relation to previous studies on protein synthesis and secretion in which 14C- and 15N-amino acids were used.

Untersuchungen zur Charakterisierung der Radioaktivitätsverteilung im Organismus bei konstanter intravenöser Infusion von Traceraminosäuren bei Ratten und zur Berechnung der Gewebeproteinsyntheserate

Male wistar rats (100 g live mass) were given infusions into the tail vein of 14C-leucine and 14C-lysine simultaneously for 0.5; 1.0; 2.0; 3.0; 4.5; 6.0 and 7.0 hours. At the end of the infusion the specific radioactivity of the free leucine and lysine in the blood plasma, liver, M. gastrocnemius, small intestines and colon were ascertained as well as after the 6-and-7-hour infusion that of the protein-bound leucine and lysine. In all tested tissues the specific radioactivity of the free amino acids attained a plateau during the 6-and-7-hour infusion. The rate constants for the increase were calculated for each organ tested. The two amino acids used are suitable for the calculation of the fractional rate of protein synthesis in tissues. The values of the fractional rate of protein synthesis calculated on the basis of the 6-and-7-hour infusion were: 54 +/- 7.7%/day for the liver, 9.4 +/- 1.2%/day for muscles, 89 +/- 12.2%/day for the small intestines and 42 +/- 5.9%/day for the colon. The simultaneous application of two tracer amino acids is recommendable for the estimation of the precursor pool for protein synthesis and the more accurate calculation of the rate of protein synthesis.

Resorption und Einbau radioaktiv markierter Aminosäuren bei Verabreichung unterschiedlicher Proteinträger an Ratten

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.

Untersuchungen zu endogenen N-Um an 15N-markierten Schweinen

Four pigs were labelled with 15N-ammonium salt over a period of 10 days in the feeding of a fishmeal diet, a fishmeal diet + partly hydrolysed straw meal, a field bean diet and a field bean diet + partly hydrolysed straw meal. The 14N-amino acids and the 15N-amino acids excreted in faeces showed highly significant correlation coefficients with the increasing content of crude fibre in the diets, which amounted to 3.0, 5.3, 10.0 and 12.1% in the DM. The following sequence was established for the growth angle (tan alpha) of the essential 14N-amino acids: Leu, Lys, Arg, Thr, Phe, Ile, Val, His and of the 15N-amino acids: Lys, Arg, Val, Leu, Ile, Thr, Phe and His. As Lys, His and Thr cannot incorporate 15N in transamination reactions in the intermediate metabolism, their level of labelling was considerable in case of diet 4. Nevertheless, tan alpha is highest for 15N-Lys and lowest for 15N-His. This means that His in contrast to Lys, parallel to increased synthesis, is also increasingly decomposed in the large intestine. In contrast to this, proline was not labelled with 15N even with the highest content of crude fibre in the diet. Despite this, 14N-proline excretion, next to glutamic acid, increased most with the growing content of crude fibre in the diet. Due to the hydrophilic character of glutamic acid and the increased water influx in the large intestine and the increased content of crude fibre in the diet, a growing proline transport parallel to the increased influx of crude fibre and water must be assumed. If the growth angle tan alpha for the excretion of 14N-amino acids is ascertained regressively for a crude fibre content of diet of 10%, one can prove from the proportion of the amino acids and a comparison from literature for faecal bacteria and ileum digesta that the amino acid composition for this measuring point largely corresponds to that of bacteria protein.

Lysinbedarfsbestimmung bei wachsenden Ratten anhand der Katabolisierungsrate von 14C- und 15N-markiertem Lysin

Male Wistar rats (weighing some 80 g at the start of the experiment) were fed diets containing maize gluten as protein carrier and which was supplemented with amino acids (except lysine) in such way that their concentrations came up to the requirement norms. Lysine was gradually supplemented this resulting in 10 diets of different lysine content (1.6-10.6 g lysine/16 g N). On the 7th experimental day, 4 animals of each group were labelled with 14C-lysine and subjected to 2-hour measuring of 14CO2-excretion. On the following day, the animals were injected i.p. 15N-lysine, the urine being collected over 24 hours to determine 15N-frequency in urine. Both 14CO2-excretion and 15N-frequency in urine were found to remain constant at a lysine content of the diet up to 4.5 g/16 g N and rose steeply from 5.8 g lysine/16 N on. Under the experimental conditions chosen the lysine requirement is deduced to be 5 g/16 g N. This method of lysine requirement determination is highly sensitive and exact because it covers the catabolization of the amino acids under study and not so parameters that are known to be influenced by other factors such as growth, N-balance, total N-conversion or CO2-formation. The method can also be applied to metabolic situations not connected with productive performances.

Methodische Untersuchungen zur stoffwechselorientierten Aminosäurenbedarfsbestimmung bei Ratten im Erhaltungszustand anhand der Oxydationsrate von 14C-markiertem Lysin zu 14CO2

Male experimental rats (100 gm liveweight) were distributed into 10 groups of 8 animals each and received balanced diets, with the exception of lysine which was added to the diets in graded amounts in such a way that the lysine content of the diets ranged from 2.44 to 5.92 gm/16 gm N. After a feeding period of 7 days the animals received 3H- and 14C lysine injected intraperitoneally, 4 animals of each group were investigated for the total CO2 excretion and 14CO2 excretion during the first 2 hrs after the injection and for the urinary excretion of radioactivity (48 hours). The remaining animals in each group were used for determining the plasma amino acids and for establishing the specific radioactivity of free lysine in the liver and muscles after an 1-hour incorporation period. Total CO2 excretion was not found to be influenced by the lysine contents while the level of excretion of 14C activity through CO2 and that of specific 14C activity of CO2 increased with increasing lysine concentrations. This produced a broken curve pattern, showing an increased release of 14CO2 (under maintenance conditions) if the diet contained 4 gm lysine/16 gm N and more. Investigations for the specific 14C activity of free lysine in the liver, the main site of lysine oxidation, showed that the increase in 14CO2 release was due to an enhanced rate of lysine catabolism and was not brought about by changes in the pool volume or in specific radioactivity. The levels of urinary 14C excretion were not found to be related to the lysine content of the diets, whereas the curve pattern of 3H excretion observed 5 to 8 hrs after injection was similar to that of 14CO2 excretion. The lysine content of blood plasma and the content of free lysine in the liver increased continuously with increasing levels of dietary lysine. The methodological studies made in the present paper showed that in scientific research a determination of amino acid requirements on the basis of CO2 oxidation data may be a very exact and sensitive method. It will also yield values for maintenance requirements.

Stoffwechselorientierte Aminosäurenbedarfsbestimmung anhand der Katabolisierungsrate von 14C- und 15N-markiertem Lysin im Erhaltungszustand

Male Wistar rats (of 60 g live weight) allotted in 10 groups were fed diets with gradually increasing lysine levels ranging from 1.4 to 7.4 g lysine/16 g N. Feed intake was restricted so much that the experimental animals did not change their live weights during the last 3 days of the 8-day experiment period. On the 7th experimental day, 4 animals of each group were injected i.p. 14-C-L-lysine, the 14CO2-excretion being subsequently measured over a period of 2 hours. On the next day, 6 animals of each group were applied an i.p. injected of 15N-L-lysine, the urine being collected over the following 24-hour period to measure the 15N-frequency. Applying both labelling methods, an increased catabolisation of the amino acid was observed after the metabolically necessary lysine requirement had been covered. The methods are very sensitive and revealed, under the experimental conditions chosed, a lysine requirement coverage of about 3 g lysine/16 g N. The possibility of using also 15N-labelled compounds in the metabolism-oriented amino acid requirement determination is likely to facilitate the transfer of the methodology to farm animals and would thus allow to study the amino acid requirement of man. The metabolism-oriented amino acid requirement determination will likewise allow to estimate exact amino acid requirement data under conditions that cannot be rated on the basis of productive yields.

Flow of endogenous and exogenous amino acids along the gut of pigs

Digesta were collected from 5 pigs of 33 kg live weight fitted with re-entrant cannulas in the duodenum (within 20-30 cm of the pylorus) and terminal ileum. The pigs received a diet of barley, soya bean oilmeal and a vitamin and mineral mixture. The flow rates of digesta, total nitrogen and the individual amino acids were measured at different time after feeding and during two 24 h periods. A marked increase in the flow of digesta, nitrogen and amino acids was seen in the duodenum after feeding. Total flow during 24 h of nitrogen and amino acids except His, Val, Leu, Phe and Met exceeded intake. Output of nitrogen and amino acids from the duodenal cannula was 117 and 108% of intake, respectively. A method to calculate the ratio of endogenous amino acids in digesta based on the amino acid composition of digesta, diet and endogenous secretions was developed. The calculated amounts of endogenous amino acids passing the proximal duodenum and terminal ileum were 32.2 and 21.9 g per 24 h, respectively. The greatest amount of endogenous amino acids passed through the duodenal cannula in the first two hours after feeding (2-3 g/h) and then gradually decreased to 1 g per hour. The results are discussed in relation to other studies on the secretion of endogenous protein and its amino acid composition.