[Studies on amino acid resorption and on level of endogenous nitrogen excretion in rats]

Proteic-anabolic capacity in rats--influence of the quality and quantity of dietary protein

The effect of quality (casein + 5% DL-methionine, normal or heated at 180 degrees C for 20 min) and quantity (4%, 6%, 10%, 15% and 20%) of dietary protein on food intake, weight increase and nitrogen retention, has been studied in both sexes weaning Nestle rats. Our results show that food intake, when expressed as g dry matter/100 g body weight and day, is not dependent on the quality and quantity of dietary protein. Weight increase goes up at a 10% dietary protein level. At higher protein levels (15% and 20%) values are only maintained. Protein quality do not cause any difference. Nitrogen retention goes up on increasing dietary protein level, with a maximum at 10% casein-methionine and 15% heated protein, being retention heated casein-methionine significantly lower. At a higher protein level, the maximal anabolic capacity for protein is maintained. Maximum Protein Productive Value (PPV) is obtained from diets containing 10% protein level (normal or heated). There is a significant decrease at higher protein levels (15% and 20%). The PPV of heated casein-methionine is lower than PPV of normal one at 6%, 10%, 15% and 20% protein levels. The results state that in our assays, in spite of the good quality of heated casein-methionine, its metabolic efficiency is below non heated protein values even when protein contribution is increased. We can assume that protein quantity is not a balancing factor for protein quality.

[Investigations of the connection between the quality of protein, the protein level and endogenous N-excretion]

The influence of various protein qualities as well as of different levels of protein on the amount of endogenous N-excretion, metabolic fecal nitrogen (MFN) and endogenous urinary N (EUN) was determined at growing albino rats. The test rations were labelled with admixtures of 15N-DL-methionine resp. 15N-DL-lysine or contained feed protein enriched with 15N. EUN and MFN and their sum (the N maintenance requirement) showed the influence of the respective protein source and its dependence on the protein level. The endogenous N-excretions showed an opposite tendency to the N-balance; for high-quality protein feedstuffs with a high N-balance (e.g. dried eggs) they are lower than for protein source of inferior quality, with a low N-balance only (e.g. wheat gluten). Presumably this interaction of retention and maintenance is due to the complementary effect of exogenous and endogenous amino acids in the N-resp. amino acid-pool. Provided that the N-dose and the liver weight of the animals are comparable, the N-balance appears to be more suitable as parameter for the description of the protein quality and the calculation of the protein utilisation than N-retention, as the sum of N-balance and the values of MFN and EUN (depending on the feedstuffs and the N-level).

[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.

[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.