Effect of diet and essential amino acids gavage on young rat amino acid metabolism enzymes

• 1.1. The effects of a high-fat, high-energy diet and essential plus semi-essential amino acid gavage on pup rats have been studied (60–65 animals).
• 2.2. The activities of alanine transaminase, adenylate deaminase, glutamine synthetase and serine dehydratase have been tested in liver and muscle.
• 3.3. Plasma was used for the estimation of proteins, urea, amino acids, glucose, lactate, 3-hydroxy-butyrate and acetoacetate.
• 4.4. Liver and muscle glutamine synthetase activities are increased by diet and gavage administered. Hepatic serine dehydratase is inhibited by a cafeteria diet but activated by amino acid gavage. Adenylate deaminase is inhibited by diet and gavage in the liver, but gavage does not affect this enzyme activity in muscle. Liver alanine transaminase is increased by the diet; in the muscle, cafeteria diet and amino acid gavage showed the highest values for this enzyme.
• 5.5. In the plasma, the increase in lactate produced by the diet is inhibited by the amino acids provided. Cafeteria-fed pups showed lower urea levels and higher 3-hydroxybutyrate concentrations in the plasma.
• 6.6. Intracellular glucose is diminished by cafeteria diet. In contrast, the blood cell amino acid concentration increases with diet and gavage supplied.

     

Effect of starvation and a protein diet on the amino acid metabolism enzyme activities of the organs of domestic fowl hatchlings

The activities of alanine and aspartate transaminases, adenylate deaminase, glutamine synthetase and glutamate and xanthine dehydrogenases have been measured in liver, yolk sac membrane, intestine and breast and leg muscle of domestic fowl hatchlings receiving for 3 or 5 days either a standard diet or hard boiled eggwhite as well as in 3 or 5 days starved animals. The patterns of activation of amino acid metabolism enzymes were fully comparable in protein-fed and starved groups with respect to fed controls; the differences with respect to the latter became more marked in 5- than in 3-days old chicks. In 5-days old chicks intestine alanine transaminase activity increased in parallel to that of liver in protein-fed animals but not in those starved, in agreement with an enhanced alanine transfer between both organs under this situation. Both, starvation and protein-feeding, induced a general decrease in the amino acid metabolizing ability of muscle. Glutamine (but not alanine) synthetizing capabilities were enhanced.     

The effects of starvation on plasma free amino acid and glucose concentrations in lake sturgeon

The effect of starvation on the metabolism of the lake sturgeon Acipenser fulvescens was examined by measuring haematocrit, plasma glucose concentrations, and plasma free amino acids. Plasma was sampled on day 0, 10, 20, 45 and 60 of a 60-day starvation period. Haematocrit was observed to decrease with starvation indicating a decreased oxygen carrying capacity of the blood. Plasma glucose levels differed only at day 10, with a decrease in blood glucose level in the starved group. No differences were detected between groups for alanine, aspartate, and serine, while elevated levels were observed for glutamine throughout the experiment. An increase in arginine, tyrosine, valine, methionine, tryptophan, phenylalanine, glutamate, glycine, isoleucine, histidine and leucine, concentrations were observed after 45 days of starvation. The maintenance, or increased plasma levels, of glucogenic amino acids in combination with the maintenance of blood glucose concentrations indicates active gluconeogenic processes in the liver supported by muscle proteolysis.     

Naphthol-yellow-S protein content of individual rat hepatocytes as related to food intake and short-term starvation

With regard to the protein content, as analysed cytophotometrically, of hepatocytes from rats kept under a 12L 12D photoperiod (photophase 7:00-19:00), the following facts have been established: 1) Hepatocytes of different classes of ploidy all demonstrate, more or less equally, daily variations in protein content and also its reduction after 24-h fasting. 2) With computer analysis of data obtained at eight time points during a period of 24 h, a sinusoidal curve of the protein content of individual mononuclear tetraploid hepatocytes throughout the day could be demonstrated with a maximum at 6:20 and a minimum at 18:20. 3) Animals, fed with meals via a dispensing machine from 23:00 to 24:00 only, show a similar sinusoidal curve but with higher amplitude, and a virtually identical mean value as those fed ad libitum. The maximum was found at 10:40, revealing a time lag of 12 h after food intake, the minimum at 22:40. 4) Trained animals deprived of food during the standardized feeding time revealed a moderate reduction of their hepatocyte protein content in the first 6 h, then a 6-h period with a steep fall followed by a slower reduction. After 24 h, the mean hepatocyte protein mass had decreased to 72% of that at the commencement of fasting at 23:00.     

The effect of insulin deficiency, dietary protein intake, and plasma amino acid concentrations on brain amino acid levels in rats

The effect of diabetes (streptozotocin, 65 mg/kg ip), dietary protein intake (15-60%), and plasma amino acid concentrations on brain large neutral amino acid levels in rats was examined. After 20 days, the plasma concentrations of methionine and the branched chain amino acids (BCAA), valine, isoleucine, and leucine were increased in diabetic rats. In brain tissue, methionine and valine levels were increased but threonine, tyrosine, and tryptophan concentrations were depressed. Increased protein consumption promoted a diabetic-like plasma amino acid pattern in normal rats while enhancing that of diabetic animals. However, with the exception of threonine, glycine, valine, and tyrosine, there was little effect on brain amino acid levels. A good association was found between the calculated brain influx rate and the actual brain concentration of threonine, methionine, tyrosine, and tryptophan in diabetic animals. There was no correlation, however, between brain influx rate and brain BCAA levels. Thus, the brain amino acid pattern in diabetes represents the combined effects of insulin insufficiency and composition of the diet ingested on plasma amino acid levels as well as metabolic adaptation within the brain itself.     

Derepression of amino acid transport by amino acid starvation in rat hepatoma cells.

Amino acid starvation causes an adaptive increase in the initial rate of transport of selected neutral amino acids in an established line of rat hepatoma cells in tissue culture. After a lag of 30 min, the initial rate of transport of alpha-aminoisobutyric acid (AIB) increases to a maximum after 4 to 6 h starvation of 2 to 3 times that seen in control cells. The increased rate of transport is accompanied by an increase in the Vmax and a modest decrease in the Km for this transport system, and is reversed by readdition of amino acids. The enhancement is specific for amino acids transported by the A or alanine-preferring system (AIB, glycine, proline); uptake of amino acids transported by the L or leucine-preferring system (threonine, phenylalanine, tyrosine, leucine) or the Ly+ system for dibasci amino acids (lysine) is decreased under these conditions. Amino acids which compete with AIB for transport also prevent the starvation-induced increase in AIB transport; amino acids which do not compete fail to prevent the enhancement. Paradoxically threonine, phenylalanine, tryptophan, and tyrosine, which do not compete with AIB for transport, block the enhancement of transport upon amino acid starvation. The starvation-induced enhancement of amino acid transport does not appear to be the result of a release from transinhibition. After 30 min of amino acid starvation, AIB transport is either unchanged or slightly decreased even though amino acid pools are already depleted. Furthermore, loading cells with high concentrations of a single amino acid following a period of amino acid starvation fails to prevent the enhancement of AIB transport, whereas incubation of the cells with the single amino acid for the entire duration of amino acid starvation prevents the enhancement; intracellular amino acid pools are similar under both conditions. The enhancement of amino acid transport requires concomitant RNA and protein synthesis, consistent with the view that the adaptive increase reflects an increased amount of a rate-limiting protein involved in the transport process. Dexamethasone, which dramatically inhibits AIB transport in cells incubated in amino acid-containing medium, both blocks the starvation-induced increase in AIB transport, and causes a time-dependent decrease in transport velocity in cells whose transport has previously been enhanced by starvation.     

Effect of triperidol on carbohydrate and amino acid metabolism in rat brain-cortex slices

1. The effect of triperidol on the metabolism of glucose, pyruvate, glutamate, aspartate and glycine was studied with rat brain-cortex slices, U-¹⁴C-labelled substrates and a quantitative radiochromatographic technique. 2. Triperidol at a concentration of 0·2mm decreased the oxygen uptake and the ¹⁴CO₂ production by about 30% when glucose, pyruvate and glutamate were used as substrates, whereas no effects were observed with aspartate and glycine. 3. The drug did not alter qualitatively the metabolic pattern of the substrates. 4. Quantitatively, triperidol decreased the incorporation of ¹⁴C from [U-¹⁴C]glucose and [U¹⁴-C]-pyruvate into glutamate, glutamine and γ-aminobutyrate but not into lactate, alanine and aspartate. The overall utilization rates of glucose and pyruvate were decreased. The relative specific radioactivities of glutamate and aspartate were also decreased. 5. Triperidol increased the rate of disappearance of U-¹⁴C-labelled glutamate, aspartate and glycine from the incubation medium, and altered the distribution of their metabolites between medium and tissue. 6. No appreciable effect of triperidol on [1-¹⁴C]galactose disappearance was found.     

Effect of extreme amino acid starvation on the protein synthetic machinery of CHO cells.

When CHO cells are incubated under conditions of extreme amino acid starvation, effected by withdrawal of an amino acid from the medium together with genetic or chemical interference with the activity of the corresponding aminoacyl-tRNA synthetase, there is a rapid and profound decline in the functional capacity of the protein synthetic machinery. The effect was observed for all amino acids tested including leucine, asparagine, histidine, methionine and glutamine. This decline in protein synthetic potential appears to be due to a progressive permanent inactivation of the specific aminoacyl-tRNA synthetase concerned, as shown by a decline in the amount of cellular, specific aminoacyl-tRNA and a decline in the cell-free enzyme activity, measured after reversal of the starvation conditions. When cells are left for more than several hours under these starvation conditions, they shrink in size, lose viability and eventually disintegrate, with anomalous rapidity. We suggest that the progressive loss of protein synthetic capacity of the cells is the prime cause of these subsequent events. If the starvation conditions are reversed before cell death, regeneration of the protein synthetic potential occurs rapidly but requires protein synthesis itself, implying the existence of strong control mechanisms for cellular aminoacyl-tRNA synthetase activities.     

The effects of cafeteria diet induced obesity on rat blood amino acid compartmentation.

In female virgin Wistar rats, the effects of a cafeteria-diet induced obesity on blood amino acid levels and their distribution between plasma and blood cells have been studied in fed and 24-hour starved states. Cafeteria diet induced obesity provoked a decrease in total blood cell amino acid content, both in fed and starved situations when compared with controls. Whether is a causal factor for developing obesity due to imbalance in tissue amino acid supply for protein biosynthesis processes, or represents some signal related to hypothalamic control of feeding, or is a consequence of the obesity remains to be established.     

Direct effects of proteasome inhibitor AdaAhx3L3VS on protein and amino acid metabolism in rat skeletal muscle

Proteasome inhibitors are novel potential drugs for therapy of many diseases, and their effects are not fully understood. We investigated direct effects of peptide vinylsulfone inhibitor AdaAhx3L3VS on protein and amino acids metabolism in rat skeletal muscle. Soleus and extensor digitorum longus muscles were incubated in a medium containing 30 micromol/l AdaAhx3L3VS or no inhibitors. Total proteolysis was determined according to the rates of tyrosine release into the medium during incubation. The rates of leucine oxidation and protein synthesis were evaluated during incubation in medium containing L-[1-14C]leucine. Amino acid concentrations in the medium were measured using HPLC. AdaAhx3L3VS decreased tyrosine release into the medium by 21 and 19 %, decreased leucine incorporation into proteins by 22 and 12 %, and increased leucine oxidation by 24 and 19 % in soleus and extensor digitorum longus muscles, respectively. The release of amino acids into the medium was reduced. We conclude that AdaAhx3L3VS significantly decreased proteolysis and protein synthesis and increased leucine oxidation.     

Effect of 36-hour starvation on in vivo amino acid and glucose uptake by rat brown adipose tissue

The effect of 36-hour starvation on the net uptake/release of amino acids and glucose by interscapular brown adipose tissue (IBAT) of the rat has been studied by means of the determination of the arterio-venous differences in their blood concentrations. Starvation induced a net release of non-essential amino acids by the tissue, mainly alanine, glutamine, glycine and citrulline. In food deprived animals there was not a net glucose uptake by the IBAT. The results obtained in this study are in accordance with a typical peripheral tissue metabolic pattern of IBAT under food deprivation situations.     

Effect of amino acid starvation on glucose transport in two archaeal organisms

When protein synthesis is arrested by amino acid starvation, Escherichia coli wild-type strains show stringent control (SC) over stable RNA (sRNA) accumulation as well as a large number of other growth-related processes. One of the events under SC is transport of metabolites. Thus, under amino acid starvation, E. coli fails to accumulate the non-metabolizable glucose analog alpha-methyl-D-glucoside, whereas isogenic relaxed strains continue to take up this glucose analog. Unlike the Bacteria, most wild-type archaeal strains show relaxed control of sRNA accumulation, although a number of stringent strains have been identified. In order to determine whether stringency in the Archaea affects physiological events different from sRNA accumulation, transport of glucose analogs was examined under amino acid starvation in two stringent archaeal strains, Haloferax volcanii and Sulfolobus acidocaldarius. The experiments were performed with 2-deoxy-D-glucose, which was shown to be transported, but metabolized very limitedly. Unlike E. coli, H. volcanii and S. acidocaldarius continued to transport 2-deoxy-D-glucose under amino acid starvation. Thus, in both Archaea glucose analog transport is not under SC, as it is in E. coli.     

Effect of amino acid starvation on UV sensitivity ofLactobacillus acidophilus cells

InLactobacillus acidophilus cultures UV irradiated in the exponential phase of growth, the dosesurvival curve was of the simple exponential type, without any shoulder. If the bacteria were subjected to amino acid starvation prior to irradiation, an shoulder corresponding to a quasi-treshold dose (D_q) of about 780 ergs/mm² appeared in the curve. The administration of protein or RNA-synthesia inhibitors prior to irradiation had the same effect. The effect of pre-irradiation amino acid starvation was abolished by simultaneous thymidine starvation. It was likewise abolished if amino acid starvation was followed by incubation in the presence of amino acids (without thymidine) and then by irradiation of the cells. Post-irradiation amino acid starvation did not lead to the formation of an shoulder but if combined with thymidine starvation it did. It can be concluded from the results that post-irradiation repair processes are facilitated or promoted if, during the post-irradiation interval DNA synthesis is delayed. This delay represents a compensation of the pre-irradiation increase of cellular DNA-content, taking place during inhibition of proteosynthesis. The postirradiation administration of caffeine did not abolish the formation of the shoulder induced by pre-irradiation amino acid starvation; on the contrary, it induced its formation even in exponentially growing, irradiated control bacteria.