Studies of protein reserves. The relation between protein intake and resistance to protein deprivation

Clinical use of amino acids as dietary supplement: pros and cons

Nitrogen supply is pivotal for the maintenance of life. Amino acids can be utilized to synthesize both glucose and lipids. The opposite, i.e., production of amino acids from either one of them, is not possible in the absence of other amino acids as donors of nitrogen. The quality of amino acid content in protein has been re-evaluated recently, and the relevance of essential amino acids has been repeatedly underlined. Essential amino acid requirements in different mammals are not identical, and ratios among them should be taken into account when projecting an efficient formulation. Recent research has demonstrated that genes respond to different qualities and quantities of nutritional supply, and increased provision of essential amino acids increases lifespan in animal experiments through mitochondriogenesis and maintenance of elevated rates of synthesis of anti-oxidant molecules. Moreover, genetic expression of key controllers of synthesis, like mTOR, may be particularly important for understanding skeletal muscle maintenance. Losses of muscle mass and impaired immune function are related to reduced protein supply, and there is increasing evidence that regular essential amino acid intake as part of an oral diet is effective in reversing muscle catabolism, promoting muscle anabolism, and restoring immunological function. Therefore, the use of amino acids as supplements to diet would be expanding in the near future. Is this safe? Few data are available on amino acid toxicity, and only one essential amino acid may be considered to have clinically relevant toxicity: methionine, because it is transformed into a toxic intermediate, homocysteine, when cysteine synthesis is required by metabolic needs. Matching of stoichiometric ratios between methionine and cysteine may solve the problem of supplying sufficient amounts of sulfur to the body. Arginine and glutamine are two non-essential amino acids than can become "conditionally essential" because of elevated needs during pathological conditions, and metabolism may not be able to maintain their concentrations at sufficient levels to match metabolic requirements. Chronic exogenous arginine supplementation has not proven to exert positive clinical effects in different trials, and sequential articulation of the knowledge of introduction of arginine-driven transcriptional, translational, and epigenetic adaptations may give us a key for interpreting those puzzling results.

Studies on nitrogen metabolism in rats of different age fed on a protein-free diet. 3. Urinary endogenous nitrogen excretion in relation to body size and protein-free feeding duration

The influence of the time (t = 3, 6, 9, 12 and 16 days) of feeding on a protein-free diet (PFD) and the size of shrunk body mass (SB), increasing with age but decreasing with the duration of feeding on PFD, on the excretion of endogenous urinary nitrogen (EUN) were investigated. The experiment was on 350 male rats from 23 to 275 days of age and mean SB from 39 to 430 grammes, divided into 14 age groups (k = 14). The material and the method of the experiment as well as the composition of PFD were described in detail in part one of this work (Beza, 1986). The linear analysis of covariance showed that the EUN excreted after 3, 6, 9, 12 and 16 days on PFD as well as the average daily EUN did not significantly correlate with the initial body mass (SBi). It were calculated: 1. In relationship EUN(t) the slope ratios bk and intercepts ak, differed between the groups of age significantly. The ak values but not the bk, were closely correlated with the initial body mass SBi (r for ak values = 0.947***) indicating that the amount but not the rate of EUN excretion was closely related to SBi; 2. the daily EUN excretion at 1, 3, 6, 9, 12 and 15 days on PFD in relation to body mass in these days-EUNd(SBd) is described by the equation: EUNd = Ad.SBd 0.872 less than 1, in which Ad decreased from 287 mg N/SBd 0.872 on the first day to 167 mg N/SBd 0.872 on the 15th day on PFD; 3. the daily excretion of EUN(y) in relation to the daily body mass (x1) and to the day on PFD (x2) is described by the equation: EUNd(y) = 286.8.x1(0.872).x2(-0.1993); R = 0.987*** with N in mg, SB in kg. There was a directly proportional relationship between EUNd and SB0d 0.872 only (b1 = 1), whereas between EUNd and SBd 0.67 as well as between EUNd and SBd 0.75 the slope ratios b1 were 1.308 and 1.163, respectively and were significantly higher than one. With prolonged feeding on PFD for 15 days, the rate of EUNd excretion decreased in accordance to b2 = -0.1993 less than 0**, independently of the age and the initial SB of the rats.(ABSTRACT TRUNCATED AT 400 WORDS)

[Growth and hematological criteria of rats by different protein and iron supply]

In a two-factorial experiment with growing rats, protein content of diet (5, 25, 45%) and Fe supply (5, 25, 625 mg/kg diet) were changed. Both factors as well as their interactions influenced growth (p less than 0.001). The growth was reduced especially by deficient protein supply but although by inadequate iron supply and in a smaller degree by an excessive protein content of the diet. Hematological values as hemoglobin content, counts and volume of erythrocytes, hematocrit, MCH and MCHC - measured after 35 days of the experiment - were influenced by both factors and their interactions, too (p less than 0.001). Again deficient protein supply and insufficient Fe supply have the marked effects. Referring life weight as well as hematological parameters, the deficient protein supply was - independent of Fe supplementation - the limited factor, whereas in the cause of higher protein content (25, 45%) an insufficient Fe supply has negative effects.

[Effect of graduated protein supply (0-50%) on hematologic values as well as protein and urea concentrations in the plasma of rats]

The influence of graduated protein supply (0-50% casein) on hematological values was studied in growing rats and compared with other criteria of the supply status. The following results were obtained: Weight development was found to reflect to 30%, the plasma protein content to 40% the level of protein supply. The highest protein levels revealed a trend towards lower values. At a dietary protein content of 15 to 20%, the urea concentrations of plasma went through a minimum. Both with better and with poorer protein supply they proved higher thus suggesting an increasingly energetic conversion of the feed protein. The hematological values hemoglobin, hematocrit and erythrocyt number responded uniformaly to the level of protein supply. This is also attributable to the close statsitical relationship between these three magnitudes. Whilst at the end of the experiment the erythrocyt number with protein-free diet proved lowest, the smallest values for hemoglobin and hematocrit were observed with 5% protein. From 10% on the differences were not so marked. Especially high values were measured, however, for all criteria at 40 and 50%, partly at 25% protein. As the calculation of the mean cell volume (MCV) revealed, insufficient protein supply is likely to affect rather the erythrocyt ripening than iron conversion. In agreement with this idea, the mean corpuscular hemoglobin concentration (MCHC) was not found to be influenced by protein supply.