Absorption and metabolism of butyric acid in rabbit hind gut

Butyrate absorption in the large intestine of the rabbit was evaluated by the variation of concentrations in the bowel, the arterio-venous plasma and the intestinal loops. The metabolic transformations were studied with (3-4 C14) butyrate. The caeco-colonic epithelium oxidized negligible quantities of butyrate to ketone bodies and other metabolic pathways were found. These pathways were of different intensity according to the region of the gut and both phases of the excretory cycle. A portion, which may be large, was metabolized in the caeco-colonic wall and in the liver where radioactivity was found in free amino acids, carboxylic acids and sugars. The oxidation to CO2 in TCA cycle yields energy for metabolic activities. This study of metabolism takes account of the endoflora participation.     

Effects of plasma aldosterone on butyrate absorption and metabolism in the rabbit proximal colon

Butyrate absorption in the proximal colon of the anaesthetized rabbit was evaluated by measuring the variations in the concentration of butyrate in colonic loops and in arterial and venous plasmas; metabolic conversions were studied using (3,4-14C) butyrate. Interrelations between butyrate absorption and metabolism and the excretory cycle of the rabbit were examined, as well as the effects of exogenous aldosterone, the hormone generally implicated in the diurnal rhythm of the fecal excretion. The colonic tissue metabolized butyrate via 2 main pathways. They were of differing intensity according to the 2 phases of the excretory cycle. When the plasma level of aldosterone was high (during hard faeces production), the butyrate was mainly oxidized to CO2, yielding energy for metabolic processes. When the plasma level of aldosterone was lower (during soft production), butyrate was also oxidized to CO2 but it was a better source of free amino acids. Exogenous aldosterone (30 micrograms/kg) enhanced absorption and oxidative metabolism of the butyrate, which occurred normally when hard faeces were elaborated.     

Splanchnic and peripheral uptake of amino acids in relation to the gut

There are many complexities and theoretical aspects to consider for studies of amino acid absorption and metabolism by the gut, liver, and peripheral tissues. The experimental approach must vary depending on the amino acid. Whether to sample whole blood or plasma has to be considered carefully. Also, a specific blood vessel has to be chosen for taking samples. A jugular vein can be the poorest sampling site for many studies. The amounts of individual amino acids appearing in portal blood are different from amounts disappearing from the gut lumen. Some are absorbed in amounts equal to that disappearing but most are absorbed in lesser quantities because of intestinal metabolism. Further, the liver removes absorbed amino acids and synthesizes plasma proteins, urea, and glucose. Peripheral tissues, of course, exchange amino acids with protein for normal turnover but also use amino acids for oxidation and transamination. Alanine, glutamine, glycine, and arginine are important in transporting nitrogen out of peripheral tissues in a nontoxic form. Branched-chain amino acids are removed by both liver and peripheral tissues mainly for plasma protein and ketoacid formation, respectively. During fasting, however, muscle releases branched-chain amino acids while removal by liver is maintained.     

Changes in the proteolytic activity of tissues during aging

The intensity of proteolytic processes and qualitative composition of autolysis products of the brain, liver and testicle tissues of young and old rats were studied. The gel-chromatographic analysis (Sephadex G-15 and G-50) revealed no considerable amount of high-molecular peptides (1500 Da and over) before and after autolysis. The measurement of the quantity of free amino groups in the gel-chromatographic fraction after the complete acid hydrolysis has confirmed that result. The low-molecular peptides and free amino acids, are the main products of the tissue autolysis. The intensity of proteolytic processes, determined by an increase in the amount of amino acids depends on the autolysis duration and age of animals. The total increment of amino acids in the brain and liver tissues of old animals for the first hour of autolysis has been higher by 102 and 219% as compared to young ones. The autolysis of testicles of the young and old animals after the first hour of incubation is characterized by the same intensivity. Such a regularity is not revealed when analyzing the same processes by the Lowry method.     

Substrates of Energy Metabolism of the Pituitary and Pineal Glands

The capability of the neurohypophysis, the adenohypophysis, and the pineal gland to oxidize nonesterified fatty acids and glucose as energy sources was studied in vivo. Fed and 48-h-starved rats had catheters placed in their femoral vessels. After they became conscious, an intravenous injection of one of the following was given: [1-14C]acetate, [1-14C]octanoate, [1-14C]-palmitate, or [2-14C]glucose. After 5 min the rats were sacrificed. These metabolites produce [14C]acetyl-CoA within the mitochondria when they are oxidized as metabolic fuels. On passage through the Krebs cycle a considerable portion of the 14C is trapped in large amino acid pools closely associated with the Krebs cycle; the appearance of 14C in these amino acids was taken as evidence of oxidation. As expected, brain structures behind the blood-brain barrier (cerebral cortex and caudate) showed considerable labeling of Krebs cycle-associated amino acids in both nutritional states when [2-14C]glucose was the substrate. Surprisingly, however, no label was detected in amino acids of the neurohypophysis or the pineal gland in starved rats and very little in fed rats. On the other hand, 14C from acetate and palmitate was extensively incorporated into amino acids of the pineal gland and the neurohypophysis, while little 14C labeling was found in the cerebral cortex and the caudate. Octanoate, which passes the blood-brain barrier readily, labeled amino acids of all tissues. The experiments demonstrated conclusively that the neural structures studied, which have no blood-brain barrier, do not rely heavily upon glucose as a fuel for oxidative energy metabolism, in contrast to the rest of the brain. The results also showed that nonesterified fatty acids may supply at least some of their energy requirements.     

Systemic multicompartmental effects of the gut microbiome on mouse metabolic phenotypes

To characterize the impact of gut microbiota on host metabolism, we investigated the multicompartmental metabolic profiles of a conventional mouse strain (C3H/HeJ) (n=5) and its germ‐free (GF) equivalent (n=5). We confirm that the microbiome strongly impacts on the metabolism of bile acids through the enterohepatic cycle and gut metabolism (higher levels of phosphocholine and glycine in GF liver and marked higher levels of bile acids in three gut compartments). Furthermore we demonstrate that (1) well‐defined metabolic differences exist in all examined compartments between the metabotypes of GF and conventional mice: bacterial co‐metabolic products such as hippurate (urine) and 5‐aminovalerate (colon epithelium) were found at reduced concentrations, whereas raffinose was only detected in GF colonic profiles. (2) The microbiome also influences kidney homeostasis with elevated levels of key cell volume regulators (betaine, choline, myo‐inositol and so on) observed in GF kidneys. (3) Gut microbiota modulate metabotype expression at both local (gut) and global (biofluids, kidney, liver) system levels and hence influence the responses to a variety of dietary modulation and drug exposures relevant to personalized health‐care investigations.     

Amphioxus allantoicase: molecular cloning, expression and enzymatic activity

Allantoicase, one of the purine metabolism enzymes, is progressively truncated during the chordate evolution, yet it is unknown when its activity became phylogenetically extinct. In this study, a cDNA encoding allantoicase was isolated from the gut cDNA library of amphioxus Branchiostoma belcheri tsingtauense. It is 2441 bp long, and contains an open reading frame encoding a protein of 392 amino acid residues. RT-PCR analysis showed that amphioxus allantoicase was strongly expressed in the hepatic caecum, and weakly expressed in other tissues including hind-gut, gill, muscle, notochord, testis and ovary. The parallel experiment was performed measuring the allantoicase activity in the same tissues revealed that its activity was high in the hepatic caecum, but low or undetectable in other tissues examined. These suggest that allantoicase remains in action in the primitive chordate amphioxus.     

Incorporation of Acetate into Acetylcholine, Acetylcarnitine, and Amino Acids in the Torpedo Electric Organ

The metabolism of acetate was investigated in the nerve-electroplaque system of Torpedo marmorata. In intact fragments of electric organ, radiolabeled acetate was incorporated into acetylcholine (ACh), acetylcarnitine (ACar), and three amino acids: aspartate, glutamate, and glutamine. These compounds were identified by TLC, high-voltage electrophoresis, column chromatography, and enzymic tests. The system responsible for acetate transport and incorporation into ACh displayed a higher affinity but a lower Vmax than that involved in the synthesis of ACar and amino acids. Choline, when added to the medium, increased the rate of acetate incorporation into ACh but decreased (at concentrations greater than 10(-5) M) that into ACar and amino acids. Monofluoroacetate slightly depressed ACh and ACar synthesis from external acetate but inhibited much more the synthesis of amino acids. During repetitive nerve stimulation, the level of the newly synthetized [14C]ACh was found to oscillate together with that of endogenous ACh, but the level of neither [14C]ACar nor the 14C-labeled amino acids exhibited any significant change as a function of time. This means that there is probably no periodic transfer of acetyl groups between ACh and the investigated metabolites in the course of activity. Acetate metabolism was also tested in the electric lobe (which contains the cell bodies of the neurons innervating the electric organ) and in Torpedo synaptosomes (which are nerve terminals isolated from the same neurons). Radioactive pyruvate and glutamine were also assayed in some experiments for comparison with acetate. These observations are discussed in connection with ACh metabolism under resting and active conditions in tissues where acetate is the preferred precursor of the neurotransmitter.     

Changes in amino acids and protein metabolism in Egyptian cobra (Naja haje) during hibernation

1. 1.Total protein, GOT, GPT, alkaline phosphatase and total free amino acid content in the brain, liver and kidney were studied in the hibernating, arousing and normothermic cobra (Naja haje).

2. 2.Tissues showed a decline in protein content which started in the prehibernating animals. At the low body temperatures in hibernation both synthesis and degradation would be reduced. The fall in protein content suggests synthesis is reduced more steeply than is degradation. Recovery of protein biosynthesis was demonstrated during arousal.

3. 3.In aroused animals, the levels of free amino acids in the tissues examined were higher than in hibernating ones or in normothermic controls studied in summer.

4. 4.A decline in GOT activity was recorded in the hibernating animals. The enzyme activity showed recovery on arousal. A similar trend was observed for the GPT activity in brain and kidney.

5. 5.The activity of alkaline phosphatase was also examined in the different tissues. The correlation of these changes to the different phases of hibernating cycle is discussed.

Nutritional value of protein hydrolysis products (Oligopeptides and free amino acids) as a consequence of absorption and metabolism kinetics

When pigs were submitted to duodenal infusion of solutions containing a large percentage of small peptides (PEP) or free amino acids with the same pattern (AAL) amino acids appear in the portal blood more rapidly and more uniformly after infusion of PEP then after infusion of AAL, with the notable exception of methionine for which the opposite was true. These differences were lowered when a carbohydrate (maltose dextrin) was present in the solution, but nevertheless remained significant for the first hour after the infusion. The long‐term (8‐hour) uptake of free amino acids into the liver and the peripheral tissues differed in profile according to the nature of the duodenal infusion. Peripheral uptake was appreciably less well balanced after infusion of free amino acids (deficiency of threonine and phenylalanine) than after infusion of small peptides (deficiency of methionine). Accordingly, in the rat, under conditions of discontinuous enterai nutrition the mixture of small peptides was of greater nutritive value than the mixture of free amino acids. It thus appears that the absorption kinetics which results in important variations in the temporal distribution of free amino acids in the tissues may be at the origin of transitory imbalances in tissue amino acid uptake, and as a result of a lower nutritive value.     

Free amino acids in brain, liver, and skeletal muscle tissue of voles infected with Trypanosoma brucei gambiense.

The concentrations of several acidic and neutral amino acids of brain, liver, and skeletal muscle were determined in field voles, Microtus montanus, and compared to values obtained from voles harboring a chronic infection of Trypanosoma brucei gambiense. All of the amino acids examined were found at comparable levels in brain tissue from both groups of animals with the exception of tyrosine, which was reduced by approximately 45% in the infected voles. Similarly, the only difference noted in liver tissue was 32% decrease of free tyrosine in the infected animals. With respect to muscle tissue, in addition to a 45% reduction of free tyrosine in the infected voles, decreases of a smaller magnitude were also noted for threonine, glutamate, and valine. The relatively specific alteration of free tyrosine concentrations in the investigated tissues of trypanosome-infected animals suggests an alteration in host metabolism of this amino acid and/or parasite utilization.     

Metabolomics of aerobic metabolism in mice selected for increased maximal metabolic rate

Maximal aerobic metabolic rate (MMR) is an important physiological and ecological variable that sets an upper limit to sustained, vigorous activity. How the oxygen cascade from the external environment to the mitochondria may affect MMR has been the subject of much interest, but little is known about the metabolic profiles that underpin variation in MMR. We tested how seven generations of artificial selection for high mass-independent MMR affected metabolite profiles of two skeletal muscles (gastrocnemius and plantaris) and the liver. MMR was 12.3% higher in mass selected for high MMR than in controls. Basal metabolic rate was 3.5% higher in selected mice than in controls. Artificial selection did not lead to detectable changes in the metabolic profiles from plantaris muscle, but in the liver amino acids and tricarboxylic acid cycle (TCA cycle) metabolites were lower in high-MMR mice than in controls. In gastrocnemius, amino acids and TCA cycle metabolites were higher in high-MMR mice than in controls, indicating elevated amino acid and energy metabolism. Moreover, in gastrocnemius free fatty acids and triacylglycerol fatty acids were lower in high-MMR mice than in controls. Because selection for high MMR was associated with changes in the resting metabolic profile of both liver and gastrocnemius, the result suggests a possible mechanistic link between resting metabolism and MMR. In addition, it is well established that diet and exercise affect the composition of fatty acids in muscle. The differences that we found between control lines and lines selected for high MMR demonstrate that the composition of fatty acids in muscle is also affected by genetic factors.     

Amino acids modulates the intestinal proteome associated with immune and stress response in weaning pig

The objective of this study was to investigate the effects of free amino acids supplementation to protein restricted diet on the intestinal morphology and proteome composition in weaning pigs. Weanling piglets were randomly fed one of the three diets including a corn-soybean based control diet and two lower protein diets with or without free amino acids supplementation for 2 weeks. The jejunum samples of piglets were collected for morphology and proteome analysis. Compared with the control diet, the protein restricted diet had a significant lower average daily gain and higher feed conversion rate. Free amino acids supplementation to the protein restricted diet significantly improved average daily gain and higher feed conversion rate, compared with the protein restricted diet. The villous height in pigs fed the protein restricted diet was lower than that of the control and free amino acids diet. Using two-dimensional gel electrophoresis and mass spectrometry, we identified 16 differentially expressed protein spots in the jejunum of the weaning piglet. These proteins were related to stress and immune response, the metabolism of carbohydrates and lipids, and tissue structure. Based on the proteome and ELISA analysis, free amino acids diet significantly down-regulated the jejunal expression of stress protein heat shock 60 kDa protein. Our results indicated that amino acids supplementation to the protein restricted diet could enhance weight gain and feed efficiency in weanling pigs through improving intestinal nutrient absorption and transportation, gut health, and mucosal immunity.     

Changes in plasma, tissue, and urinary nitrogen metabolites due to an inflammatory challenge

Studies were undertaken to define the changes in protein metabolism that result from stimulation of the immune system by noninfectious inflammatory agents. Chicks were injected with inflammatory agents and metabolite concentrations were determined between 4 and 48 hr postchallenge. Inflammatory agents resulted in a generalized decrease in the concentration of plasma nitrogen metabolites, including ammonia, uric acid, urea, and several amino acids. Escherichia coli and sheep red blood cell (SRBC) injections induced changes in the concentrations of tissue-free amino acids at 16 hr postchallenge. After E. coli injections, free amino acid concentrations were increased by 175% in muscle and decreased by approximately 25% in liver, spleen, and bursa. A SRBC challenge resulted in similar decreases in free amino acid concentrations in the spleen and bursa as did E. coli; however, muscle and liver free amino acid concentrations were mostly unchanged. Urinary ammonia was increased, urinary uric acid was decreased, and urinary amino acids were not affected by E. coli injection. These findings indicate that stimulation of the immune system by noninfectious inflammatory agents induces tissue-specific changes in nitrogen metabolism. Changes in amino acid pool sizes in various tissues suggest alterations in rates of protein synthesis or degradation.     

Perturbations in nitrogen metabolism of brain and liver of rat following repeated benthiocarb administration

Effects of repeated administration of benthiocarb on the nitrogen metabolism of hepatic and neuronal systems have been studied. Repeated benthiocarb treatment was associated with significant decrease in proteins with a concomitant increase in free amino acids (FAA) and specific activity levels of proteases suggesting impaired protein synthesis or elevated proteolysis. The glycogenic aminotransferases showed a significant elevation in both the tissues indicating high feeding of ketoacids into oxidative pathway for efficient operation of TCA cycle to combat energy crisis during induced benthiocarb stress. However, the activity levels of branched-chain aminotransferases decreased suggesting their reduced contribution of intermediates to TCA cycle. A comparative evaluation of the activity levels of ammonogenic enzymes, AMP deaminase, adenosine deaminase and glutamate dehydrogenase (GDH) indicated that ammonia was mostly contributed by nucleotide deamination rather than by oxidative deamination. GDH exhibited reduced activity due to low availability of glutamate. In accordance with increased levels of urea, the activity levels of arginase, a terminal enzyme of urea cycle was increased suggesting increased urea cycle operation in order to combat the increased ammonia content. As the presence of urea cycle in the brain is rather doubtful, the conversion of ammonia to glutamine for the synthesis of GABA is envisaged in brain whereas in liver, excess ammonia was converted to urea through ornithine-arginine reacting system. The increased glutaminase activity observed during benthiocarb intoxication is accounted for counteracting acidosis or maintenance of metabolic homeostasis. Arginase, a terminal enzyme of ornithine cycle showed increased activity denoting the efficient potentiality of tissues to avert ammonia toxicity. The changes observed in tissues of rat administered with benthiocarb reflects a shift in nitrogen metabolism for efficient mobilization of end products of protein catabolism.     

Distribution of nutrient reserves during spinning in tissues of the larva of the fly, Rhynchosciara americana

The amount of protein, carbohydrate, lipids, and free amino acids were examined in the spinning stage in the fat body, haemolymph, skeletal muscle, and gut of Rhynchosciara americana. Protein and lipids increase in the fat body soon after the animal stopped feeding, probably at the expense of the digestion of the gut contents and of the reserves of the gut wall. Afterwards there is a fall in protein and lipids in the fat body. Haemolymph protein rises a little at the beginning of spinning and then decreases steadily during cocoon production. Carbohydrate and free amino acids decrease from the beginning of spinning in all tissues studied. Quantitatively, the most important decrease of carbohydrate during spinning occurs in the fat body whereas that of free amino acids occurs in the haemolymph. Lipid increases during spinning in the skeletal muscle, probably due to enlargement of the lateral fat body which occurs as a contaminant in the skeletal muscle preparation. The Malpighian tubules contain a large amount of calcium carbonate, which is eliminated during spinning. A correlation of our chemical data with histochemical data recently published is presented and the physiological implications of our findings are discussed in comparison to other insects.     

Metabolic adaptations to nitrogen excess in late gestation in rat.

Pregnant rats of 19th and 21st days were given an acute nitrogen overload produced by an infusion of either 0.2 M ammonium acetate or 0.2 M glutamine. Metabolic adaptations to nitrogen excess were studied measuring--in fetomaternal unit--non-protein nitrogen content and the activities of enzymes related with ammonia metabolism. Maternal and fetal plasma urea levels were increased by ammonium acetate treatment. Glutamine overload increased more the amino acid content in the mothers than in conceptus. As response to ammonium acetate treatment, glutamate dehydrogenase activity in liver was more sensitive in pregnant than in nonpregnant rats, suggesting more nitrogen incorporation into amino acids in pregnancy. Regarding glutamine synthetase activity, both treatments had an opposite effect except in kidney. The adenylate deaminase activity of pregnant rats was inhibited similarly to nonpregnant rats by nitrogen overloads, but stronger after glutamine infusion. Placenta and fetal metabolism were adjusted, as the dams, to lack of ammonia production by nitrogen overloads and to glutamine synthesis by ammonium acetate infusion.     

Fate of [14C]-glycine injected into ligated Galleria mellonella L. larvae: Formation of purines and uric acid riboside

After injection of [U¹⁴C]-glycine into the haemolymph of fully grown, ligated, and hence starving G. mellonella L. larvae, the label disappeared gradually from glycine and was found in the pool of other free amino acids, both in the haemolymph and in the tissues. The radioactivity of the free amino acid fraction diminished at a rapid rate becoming incorporated into proteins. Ten and 24 hr after injection the proteins contained 24 and 28%, respectively, of the recovered radioactivity. On the other hand, the final products of nitrogen metabolism, i.e. hypoxanthine, xanthine, uric acid and uric acid riboside initially contained only a low % of radioactivity; with time this percentage gradually increased and after 10 hr reached 12% of the total recovered radioactivity, being however always lower than that found in the protein fraction. Radioactive purines and uric acid riboside were found both in the haemolymph and in various tissues; with increasing time after injection they showed a tendency to be transferred towards the excretory organs, where they were removed with the faeces.     

Ammonia metabolism in tissue of newborn animals in health and in digestive disorders]

Ammonium nitrogen was studied for its metabolism in the tissues of ruminants in transition from pre- to postnatal development in norm and with disorders in gastroenteric digestion. It is established that the intensity of ammonium genesis and glycolysis processes as well as a cycle of tricarbonic acids change in newborn calves as compared to adult animals. The ammonium toxicosis development in sick animals, which is confirmed by an increase of the ammonia level and intensification of the reactions of ammonium- and ureogenesis in tissues of the gastroenteric tract, liver and kidneys.