Amino Acid Flux Research Articles

On the unidirectionality of arginine uptake in the yeast Saccharomyces cerevisiae

The reversibility of arginine accumulation was followed in exponentially growing cells of Saccharomyces cerevisiae and in the same cells transferred to non-growing energized conditions. Under non-growing conditions the accumulated arginine is retained in the cells while in exponentially growing cells the accumulated radioactivity is released after the addition of high external concentrations of arginine. There are indications that the process is saturable. The accumulated arginine is not exchanged for other related amino acids ( l-citrulline, l-histidine). Only l-lysine (a low-affinity substrate of the specific arginine permease) provokes partial radioactivity efflux from the cells. The switch of the arginine-related radioactive label efflux to its complete retention in the cells after changing the growth conditions occurs within a few minutes and is tentatively attributed to two concomitantly occurring events: (1) the actual presence of radioactive arginine (not its metabolite(s)) in the cell and (2) a modification of the specific arginine permease. The specific exchange of arginine described in the present study contrasts with the currently widely accepted opinion of unidirectionality of amino acid fluxes in yeast. The reasons why this phenomenon has not been observed before are discussed.

Portal-drained viscera and hepatic fluxes of branched-chain amino acids do not account for differences in circulating branched-chain amino acids in rats fed arginine-deficient diets

Concentrations and fluxes of amino acids across the portal-drained viscera (PDV) and liver were assessed in rats fed a meal of one of three arginine-deficient diets containing either alanine or the arginine precursors, ornithine or citrulline. A previous report included findings of seven arginine-related amino acids and indicated that only the citrulline-containing diet protected blood arginine concentrations. In the present report we extend these findings and note that the concentrations and fluxes of the non-arginine-related amino acids showed remarkable consistency across diet groups. However, total branched-chain amino acid (BCAA) concentrations of arterial blood were higher in rats fed the - Arg/+ Ala and the - Arg/+ Orn diets than in rats fed the control (+ Arg) diet. The elevated BCAA correlated with higher circulating concentrations of other essential amino acids but were inversely correlated with arginine concentrations. PDV and hepatic fluxes of BCAA were not different across diet groups, indicating that amino acid absorption and hepatic utilization of BCAA were generally comparable across diet groups. Hepatic concentrations of 14 of 22 measured amino acids, including total BCAA, were correlated with their arterial concentrations. The circulating concentrations and net PDV and hepatic fluxes of rats fed the control diet were comparable to our previous observations in fed rats and illustrate the role of the liver in utilization of diet-derived essential amino acids.

Volume regulation in NIH/3T3 cells not expressing P-glycoprotein. II. Chloride and amino acid fluxes.

The osmolyte function of amino acids and Cl in native NIH/3T3 cells not expressing the P-glycoprotein was examined by investigating the free amino acid concentration and the swelling-activated efflux of [3H]taurine, as representative of amino acids, and of 125I, as a tracer for Cl. Taurine and 125I efflux was activated by 20 and 30% hyposmotic solutions. At 50% hyposmotic solutions, the osmolyte pool was essentially depleted. The Cl channel blockers 5-nitro-2-(3-phenylpropyl-amino)benzoic acid, 1,9-dideoxyforskolin, dipyridamole, and niflumic acid inhibited the release of the two osmolytes by 80-95%. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (400 microM) decreased the efflux of taurine 80% without affecting that of 125I. Linolenic and arachidonic acids (5-20 microM) showed a concentration-dependent inhibitory effect on taurine and 125I fluxes. Omission of Ca decreased osmolyte fluxes by 16%. Verapamil inhibited the osmolyte release only at 500 microM. Nimodipine at 25 and 50 microM decreased the release of [3H]taurine and 125I by approximately 60 and 80%, respectively, but this effect was independent of the presence of extracellular Ca. These results indicate that amino acids and Cl function as osmolytes during regulatory volume decrease in native NIH/ 3T3 cells.

Interrelationships between amino acid and glucose metabolism in lambs of different dietary history supplemented with rumen escape protein

Changes in amino acid and glucose metabolism in response to increments of rumen escape protein (REP) were studied in groups of lambs of three differing dietary histories and consequent weights, but similar ages. Crossbred wether lambs (Merino × (Border Leicester × Merino)) were fed to obtain three distinct growth patterns. The LW group (n = 15) were offered a low quality roughage diet throughout the experiment. The MW group (n = 19) were offered a high quality mixed diet followed by the same low quality diet as LW lambs. The HW group (n = 8) were offered a high quality mixed diet throughout. All diets were offered once daily ad libitum. The LW, MW and HW groups had liveweights of 18, 32 and 41 kg respectively at the commencement of supplementation, and were 33±0·1 weeks of age. REP supplements (formaldehyde-treated casein) were offered at 0, 20, 40, 60 or 80 g/day to MW and LW lambs and at 0 or 40 g/day to HW lambs.REP increased basal digestible organic matter intake (DOMI), liveweight gain (LWG) and urinary N excretion and tended to increase N balance in LW and MW lambs. DOMI, N intake, N balance and LWG were all higher (P < 0·05) in HW compared to MW and LW lambs. REP tended (P < 0·10) to increase LWG in each dietary history group.Blood glucose concentration was higher (P < 0·01) in HW than in other lambs but was not significantly altered by REP supplementation. Irreversible loss of glucose was greater (P < 0·01) in HW lambs and increased (P < 0·001) with REP for LW and MW lambs. REP increased (P < 0·05) phenylalanine (Phe) concentration in blood, Phe flux and oxidation and whole body rates of protein synthesis and degradation. HW lambs had higher (P < 0·05) values for all these parameters than did MW and LW lambs.REP increased (P < 0·05) plasma concentrations of insulin-like growth factor-1, and plasma insulin increased (P < 0·05) in MW but not in LW or HW lambs. REP had no effect on plasma growth hormone (GH) concentration. Plasma concentration of insulin was higher (P < 0·05) in HW than in MW or LW lambs, while GH was not significantly affected by dietary history.The results show that supplementation of ruminant diets with REP increases the rate of flux and oxidation of amino acids, and the rate of glucose utilization. Amino acid supply appears to influence glucose utilization more through oxidation rate than supply, and this relationship is affected by previous dietary history (weight for age) and energy availability, either from the diet or from body stores.

The effect of abomasal infusion of casein and recombinant somatotropin hormone injection on nitrogen balance and amino acid fluxes in portal-drained viscera and net hepatic and total splanchnic blood in Holstein steers.

Six Holstein steers, 6 mo of age, with a BW range of 180 to 200 kg were used to determine effects of abomasal casein infusion and recombinant bovine somatotropin on amino acid absorption and metabolism in the gut and liver. Catheters were positioned in the hepatic vein, the hepatic portal vein, two mesenteric veins, and a mesenteric artery. Using the same basal diet, treatments consisted of 1) basal diet only (Control), 2) abomasal casein infusion of 300 g/d (Casein), and 3) abomasal casein infusion plus daily injection of 20 mg of bovine somatotropin (ST). All steers were fed the basal diet at a rate of 24 g/kg of BW on a DM basis, in 12 equal meals at 2-h intervals. Initially, Casein and ST treatments were in a balanced cross-over design, and then all steers received the Control treatment. Casein infusion tended to increase BW gain but did not affect BW gain per unit of N intake. The ST treatment increased weight gain (P < .01) and efficiency of dietary DM (P < .01) and N (P < .01) utilization by more than 40% and increased the percentage of absorbed N retained. Nonessential, essential, and total amino acid fluxes in portal-drained viscera (PDV) and their net removal by the liver were not affected by casein infusion. However, ST tended to reduce PDV flux of essential, nonessential, and total amino acids by approximately 30%, and their removal by the liver (P < .08). As a result, ST increased, compared with casein, release of essential (P < .06) and total (P < .10) amino acids from the total splanchnic pool (TSP) into peripheral blood. The ST treatment increased the availability of absorbed amino acids to peripheral tissues, but it did not affect the amino acid profile delivered from splanchnic tissues, especially that of essential amino acids.

Effect of condensed tannins in Lotus corniculatus upon the digestion of methionine and cysteine in the small intestine of sheep

SUMMARYAn experiment was conducted at Palmerston North, New Zealand, to determine the effect of condensed tannins (CT) on the true and apparent digestion of methionine and cysteine in the small intestine (SI) of sheep fed fresh Lotus comkulatus. The lotus contained c. 30 g total CT/kg dry matter (DM) and was fed hourly to sheep in metabolism crates. Four sheep were prepared with rumen and abomasal cannulae which enabled the indigestible liquid phase marker, chromium ethylene diamine tetra-acetic acid (Cr-EDTA), to be infused into the rumen to estimate digesta flow. True digestibility of plant methionine and cysteine in the SI and their site of absorption in the SI were determined from 35S-labelled L. corniculatus homogenate continuously infused into the abomasum. After 9 h infusion of the 35S-labelled lotus homogenate, the sheep were slaughtered and digesta samples were taken at intervals along the small and large intestines. The effect of CT was determined by comparing two control sheep (CT-acting) with two sheep given a continuous intraruminal infusion of polyethylene glycol (PEG, MW 3500) to bind and inactivate the CT.The CT reduced the true digestibility of plant methionine (0·72 v. 0·88) and cysteine (0·65 v. 0·81) in the SI relative to sheep receiving PEG. Condensed tannins also appeared to alter the site of digestion of both [35S]methionine and [35S]cysteine in the SI, and increased the flux of both amino acids in the mid and latter thirds of the SI. CT did not affect the apparent digestibility of total methionine (0·82 v. 0·84) in the SI but reduced the apparent digestibility of total cysteine from 0·77 to 0·66. In control sheep CT increased the abomasal flux (as a proportion of eaten) of total digesta methionine (0·88 v. 0·76) and total digesta cysteine (0·74 v. 0·62). The apparent absorption of total methionine (plant + microbial + endogenous) was increased by the action of CT (0·72 v. 0·63 g/g eaten) but was similar for total cysteine (0·49 v. 0·48 g/g eaten) in both groups. It was concluded that CT reduced the true digestibility of plant methionine and cysteine in the SI. However, it was calculated that the action of CT actually increased the total amounts (g/g eaten) of plant methionine and cysteine absorbed from the SI, due to its effect in increasing abomasal flux.

Interaction of L-cysteine with a human excitatory amino acid transporter.

1. The interaction of L-cysteine with three excitatory amino acid transporter subtypes cloned from human brain (EAAT1-3) was examined by measuring transporter-mediated electrical currents and radiolabelled amino acid flux in voltage-clamped Xenopus oocytes expressing the transporters. 2. L-Cysteine was transported by the neuronal subtype EAAT3 (EAAC1) with an affinity constant of 190 microM and a maximal rate of flux similar to that of L-glutamate; the relative efficacies (Vmax/K(m)) of the EAAT1 and EAAT2 subtypes for transporting L-cysteine were 10- to 20-fold lower. 3. Changing the ionization state of L-cysteine by raising the external pH did not significantly change the apparent affinity, transport rate, or magnitude of currents induced by L-cysteine, suggesting that both the neutral zwitterionic and anionic forms of the amino acid are transported with the same net charge stoichiometry. 4. In addition to competing with L-glutamate for uptake by the neuronal carrier, L-cysteine caused transporter-mediated release of transmitter by heteroexchange; both actions would elevate extracellular glutamate concentrations and may thus contribute to the known excitotoxic actions of L-cysteine in the brain. 5. Because the EAAT3 transporter is also expressed in tissues including kidney and intestine, the results suggest the possibility of a heretofore unrecognized mechanism of L-cysteine uptake in peripheral tissues as well as in brain.

Effect of dietary neutral detergent fiber on ileal digestibility and portal flux of nitrogen and amino acids and on nitrogen utilization in growing pigs.

Two experiments were conducted to determine the effects of dietary NDF on apparent ileal and fecal digestibility and portal flux of nitrogen (N) and amino acids, and on N retention in growing pigs. In four equal portions (at 0600, 1200, 1800, and 2400) barrows on Treatment B received a basal diet, based on casein, cornstarch, and dextrose, at a feeding level of 2.6 times energy for maintenance. Barrows on Treatment B+NDF received an additional amount of 15% (wt/wt) of purified wheat bran NDF (pNDF). In Exp. 1, four ileally cannulated barrows (40 to 75 kg) were used in a crossover arrangement comprising two treatments and three periods. The addition of pNDF decreased ileal N digestibility from 94.1 to 88.9% (P < .001), whereas ileal digestibility of most amino acids was 2 to 5.5 percentage units lower (P < .001). Utilization of ileally digested N increased from 64 to 72% with the addition of pNDF, presumably because of the contribution of pNDF to the energy supply. In Exp. 2, three barrows (30 to 54 kg) fitted with catheters in the portal vein and the mesenteric vein and artery were used in a crossover arrangement comprising two treatments and five periods. Portal absorption of nutrients was derived by multiplying the porto-arterial plasma concentration differences by portal vein plasma flow. The pNDF did not significantly affect the absorption of ileally digested amino acids and the portal flux of ammonia and urea. The results showed that addition of NDF reduced amino acid digestibility, but not the portal flux of digested amino acids, and NDF energy presumably improved utilization of ileally digested amino acids.

Quantitative aspects of blood and amino acid flows in cattle

A quantitative literature review was undertaken on the amino acid fluxes in ruminants and the factors which influence them. Two aspects were considered: blood flow and amino acid uptake by tissues. The statistical relationships indicated that blood flow was influenced by feed intake, metabolizable energy and milk production. The rates of amino acid uptake and release by tissues and organs varied greatly between compartments and between amino acids. The net rates of appearance were the result of a combination of inter- and intratissue phenomena. Simulated balances between supply and requirements revealed the limiting role of certain amino acids, depending on milk production level and growth rate. In conclusion, this approach underlined the technical difficulties involved in obtaining this type of data, and also revealed a lack of data in certain areas. Nevertheless, the observations in this review supported the implementation of the feed units used at the present time, notably for the addition of amino acids.

Effect of intraruminal propionic acid infusion on metabolism of mesenteric- and portal-drained viscera in growing steers fed a forage diet: II. Ammonia, urea, amino acids, and peptides.

This experiment investigated the effect of intraruminal infusion of propionic acid on the net flux of nitrogenous compounds across the mesenteric- (MDV) and portal-(PDV) drained viscera of seven Friesian steers, average BW 127 kg (SEM 4.6), fed a grass-pellet diet. Each received by random allocation 0 (control), .5, or 1.0 mol of propionic acid/d for 7 d. Blood flow in mesenteric and portal veins was determined by downstream dilution of p-aminohippuric acid in order to determine net appearance rates across the gastrointestinal tissues. Net urea and ammonia flux was unaffected by propionic acid supply. Circulating plasma free amino acid concentrations were increased (P < .05) by propionic acid infusion (2,235, 2,428, and 2,427, error mean square [EMS] 44,370 microM, for control, .5, and 1.0 mol of propionic acid/d, respectively). Net amino acid flux rates were increased at the highest rate of propionic acid infusion across MDV and PDV (4.66, 3.69, and 6.11, EMS 2.98 mol/d for MDV [P < .05] and 2.98, 2.45, and 3.73, EMS 1.69 mol/d for PDV [P < .10] for control, .5, and 1.0 mol of propionic acid/d respectively). Positive venous-arterio concentration differences for peptide-bound amino acids (PBAA) across the MDV and PDV indicated net appearance across the gastrointestinal tissues, but this was not affected by propionic acid infusion. The data show that amino acid flux across postruminal tissues can be influenced by ruminal propionic acid supply and that this does not affect PBAA appearance.

RBAT is an amino acid exchanger with variable stoichiometry.

The rBAT protein, when expressed in Xenopus oocytes, was previously shown to reproduce the selectivity of the Na(+)-independent neutral and basic amino acid transport system called bo,+. More recently, the capacity of rBAT to generate a transmembrane current was demonstrated when addition of neutral amino acids stimulated the efflux of cations (presumably basic amino acids) in rBAT-injected oocytes. In the present paper, aminoisobutyric acid (AIB), a neutral amino acid analogue, was shown to induce outward currents (efflux of basic amino acids) through rBAT similar to those caused by alanine in terms of affinity, maximal currents and I-V curves. Despite generating similar currents, the AIB transport rate was more than 30 times lower than that of alanine, thus challenging the assumption that rBAT functions as a classical exchanger. Experiments using a cut-open oocyte voltage clamp demonstrated that AIB was capable of stimulating rBAT-mediated currents from either side of the membrane. AIB, like alanine, was able to stimulate the efflux of radiolabeled alanine and arginine while no rBAT-mediated efflux was measurable in the absence of external rBAT substrates. These results demonstrate that (i) the presence of amino acids is required on both sides of the membrane for rBAT to mediate amino acid flux and thus rBAT must be some type of exchanger but (ii) rBAT-mediated amino acid influx is not stoichiometrically related to the efflux. A model of a "double gated pore" is proposed to account for these properties of rBAT, which contravene standard models of exchangers and other transporters.

Effects of insulin on the uptake of amino acids by hepatocytes and red blood cells from trout ( Salmo trutta) are opposite

Insulin provoked a rise in the uptake of L-alanine by isolated trout hepatocytes. This increase was dose-dependent and partially inhibited by actinomycin D and cycloheximide, suggesting that protein synthesis was involved in the hormonal action. There was an increase in the V max of the ASC system as well as in K m, but no expression of a different membrane carrier was observed. Although insulin was effective in cells from fed animals, its action was markedly higher in cells from fasted animals. Insulin had the opposite effect on red blood cells, making the incorporation of amino acids into the cell difficult as a result of a fall in the maximal capacity of uptake. This action was characteristically observed in incorporations through the ASC system, while the activity of another Na +-dependent carrier, the Gly system, was unaffected. Further, when the amino acid content of erythrocytes was in equilibrium with the extracellular concentration, insulin promoted a transient release of alanine from the cells. The physiological role of these actions of insulin may be related to the postprandial flux of amino acids from the gut to the liver.

Whole-Body Protein Turnover and Hepatic Protein Synthesis Are Increased by Vaccination in Man

1. The ability of diphtheria-tetanus-poliomyelitis-typhoid vaccination to induce modifications in protein metabolism was investigated in post-absorptive healthy humans. 2. Seven subjects were studied before and 2 days after vaccination. They underwent an intravenous primed constant infusion of L-[1-13C]leucine for 4h. Plasma protein concentrations, whole-body amino acid fluxes and acute-phase protein synthesis were determined. 3. Plasma concentrations of fibrinogen, alpha 1-acid glycoprotein, haptoglobin and alpha 1-antitrypsin were significantly elevated 2 days after vaccination (P < 0.05). Leucine oxidation was unaffected but whole-body protein synthesis and breakdown were both increased (P < 0.05), by 25 and 16% respectively, in subjects who had an elevated body temperature (n = 5). Albumin synthesis was unchanged, but hepatic synthesis of fibrinogen was 56% higher after vaccination. 4. The present investigation indicates that diphtheria-tetanus-poliomyelitis-typhoid vaccination could induce a sustained acute-phase reaction. Moreover, protein metabolism appeared to be extremely sensitive to a mild stress since leucine kinetics and fibrinogen synthesis were affected. Therefore, diphtheria-tetanus-poliomyelitis-typhoid vaccination might represent an attractive model for studying the inflammatory process in humans.

In vivo amino acid fluxes in regenerating liver after two-thirds hepatectomy in the rat

Background/Aims: Recent reports in the literaturesuggest that liver cell swelling following amino acid influx exerts anabolic and anti-catabolic effects. We have tested the possibility that rapid liver growth after partial hepatectomy is promoted by an increased amino acid-influx and that this is associated with an increased hepatic water content and a decreased rate of proteolysis. Methods: Two-thirds hepatectomy was performed in rats. Plasma liver flow and amino acid fluxes were measured after 24 or 48 h. Results: Plasma liver flow was increased 24 and 48 h after partial hepatectomy or sham-operation in pair-fed animals. At these time points, in both groups there was a specific two- to threefold increased net hepatic uptake of the amino acids alanine and glycine, both being transported by the sodium-coupled amino acid transport system A/ASC. No changes in uptake of system N transported amino acids were observed. Both in partially hepatectomized and sham-operated pair-fed animals, the hepatic uptake of alanine and glycine was accompanied by a minor increase in tissue water (from 68 to 70%). Proteolysis, measured by leucine efflux, was only reduced in regenerating livers. Conclusions: We conclude that cell swelling is not animportant factor in the stimulation of net protein synthesis during liver regeneration.

In vivo amino acid fluxes in regenerating liver after two-thirds hepatectomy in the rat

<h2>Abstract</h2><h3>Background/Aims:</h3> Recent reports in the literaturesuggest that liver cell swelling following amino acid influx exerts anabolic and anti-catabolic effects. We have tested the possibility that rapid liver growth after partial hepatectomy is promoted by an increased amino acid-influx and that this is associated with an increased hepatic water content and a decreased rate of proteolysis. <h3>Methods:</h3> Two-thirds hepatectomy was performed in rats. Plasma liver flow and amino acid fluxes were measured after 24 or 48 h. <h3>Results:</h3> Plasma liver flow was increased 24 and 48 h after partial hepatectomy or sham-operation in pair-fed animals. At these time points, in both groups there was a specific two- to threefold increased net hepatic uptake of the amino acids alanine and glycine, both being transported by the sodium-coupled amino acid transport system A/ASC. No changes in uptake of system N transported amino acids were observed. Both in partially hepatectomized and sham-operated pair-fed animals, the hepatic uptake of alanine and glycine was accompanied by a minor increase in tissue water (from 68 to 70%). Proteolysis, measured by leucine efflux, was only reduced in regenerating livers. <h3>Conclusions:</h3> We conclude that cell swelling is not animportant factor in the stimulation of net protein synthesis during liver regeneration.

Effect of mimosine on portal-drained visceral net flux and concentrations of amino acids and minerals in plasma of Alpine goats

This experiment was designed to investigate whether circulating mimosine imposes limitations on absorption of amino acids and minerals from the gastrointestinal tract of Alpine goats. Circulating mimosine, portal blood and plasma flow rate, and concentrations and net absorption of amino acids and minerals were measured 60 h before (PRE) and 24 h after (POST) the femoral vein infusion of mimosine (12.5 mg kg −1 BW −0.75 h −1). Mimosine infusion did not affect portal plasma flow rate. Venous and arterial plasma amino acid and mineral concentrations were depressed and the absorption of alanine ( P < 0.09), serine ( P < 0.04) and methionine ( P < 0.03) from the gastrointestinal tract were reduced for up to 24 h after the cessation of mimosine infusion, even when normal feeding was resumed. This disruption was possibly caused by the circulating mimosine (4.88 μm 1 −1 during POST) directly, via chelation or competition for absorption, or, indirectly, by gastrointestinal lesions resulting from circulating mimosine. Pivotal to this experiment was the observation that mimosine was eliminated from the goat circulatory system approximately 40 times more rapidly in a 24 h period than when similar concentrations were infused in sheep.

Inhibition by polyunsaturated fatty acids of cell volume regulation and osmolyte fluxes in astrocytes.

The polyunsaturated fatty acids, arachidonic, linoleic, and linolenic acids, were potent blockers of regulatory volume decrease (RVD) and of the swelling-activated efflux of [3H]taurine, D-[3H]aspartate, [3H]inositol, and 125I (used as marker of Cl) from rat cerebellar astrocytes in culture. The monounsaturated oleic and ricinoleic acids and saturated fatty acids were ineffective. The amino acid and 125I fluxes were similarly inhibited by fatty acids, whereas inositol release was less sensitive. Polyunsaturated fatty acids appear to directly affect RVD in trypsinized astrocytes as the inhibition was immediate and fully reversible. Blockers of the arachidonic acid metabolic pathways, indomethacin (cyclooxygenase), esculetin (lipoxygenases), and metyrapone (P-450 monooxygenases), did not prevent the effect of arachidonic acid, suggesting that further metabolism is not required for displaying the effects of arachidonic acid on RVD and osmolyte fluxes. Some blockers of arachidonic acid metabolic pathways, such as nordihydroguaiaretic acid (lipoxygenases) and naphthoflavone (P-450 monooxygenases), also exhibited marked inhibitory effects on RVD and on osmolyte fluxes. The predominant arachidonic acid metabolite in astrocytes, 12-hydroxyeicosatetraenoic acid, did not affect RVD or osmolyte fluxes. These results suggest that arachidonic acid and other polyunsaturated fatty acids directly inhibit the permeability pathways correcting cell volume after swelling in cultured astrocytes.

Effects of Insulin-Like Growth Factor-1 and Growth Hormone on the Net Flux of Amino Acids across the Hind Limbs in the Surgically Traumatized Pig

1. After surgery three groups of six female pigs weighing on average 52.2 kg (SD 3.5) received vehicle, recombinant insulin-like factor-1 (364.4 micrograms day-1 kg-1) or recombinant human growth hormone (467.7 m-i.u. day-1 kg-1) for two post-operative days. Vehicle and peptides were infused intravenously together with total parenteral nutrition providing 129 kJ day-1 kg-1 non-protein calories and 0.35 g N day-1 kg-1. 2. On both post-operative days the mean concentration of insulin-like growth factor-1 in arterial blood samples was clearly below presurgical levels in animals receiving vehicle or recombinant human growth hormone, whereas recombinant human insulin-like growth factor-1 infusions more than restored insulin-like growth factor-1 concentrations. These last samples, however, contained significantly (P < 0.05) less insulin than those from other animals. 3. Infusion of recombinant human growth factor was often associated with higher circulating levels of amino acids compared with recombinant human insulin-like growth factor-1 infusions. Despite this, both hormones significantly (P < 0.05) increased the hind limb net balance of total amino acids on post-operative day 1. Net balances of -44.2, +69.5 and +100.9 mumol/min (pooled SE 35.3) were associated with infusion of vehicle, recombinant human insulin-like growth factor-1 and recombinant human growth hormone respectively. This response was also closely reflected in the group of non-essential amino acids. 4. The net efflux of alanine from the hind limbs was also significantly (P < 0.002) reduced, whereas glutamine was less affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Net flux of amino acids over the hind limbs of growing pigs in relation to feeding and time of day

ZusammenfassungDie Nettobilanz von Aminosäuren in den Hinterextremitäten bei wachsenden Schweinen in Abbängigkeit von der Fütterung und TageszeitDie vorliegende Untersuchung wurde mit der Absicht durchgeführt, um diurnale Schwankungen im Blut‐Aminosäurengehalt und, um die periphere Nettobilanz von Aminosäuren zu beobachten. Dazu wurden fünf weibliche Schweine operativ mit Kathetern versehen, um Messungen von Aminosäuren‐Nettobilanzen in den Hinterextremitäten zu ermöglichen.Während einer 24‐stündigen Untersuchungsperiode wurde beobachtet, daß die Blutgehalte der Aminosäuren in den Morgenstunden vor der Fütterung um 0800 h am niedrigsten lagen, unmittelbar danach stieg der Gehalt auf ein maximales Niveau. Im Unterschied zu dieser schnellen Erhöhung stieg die Nettobilanz der gesamten Aminosäuren nur langsam von einem Minimum von 115,9 μmol/min (±104,1) zwischen 0400 und 0800 h bis zu einem Maximum von 451,9 μmol/min (SE 104,1) zwischen 2000 und 2400 h. Diese beiden Werte unterscheiden sich signifikant (p&lt;0,05) voneinander. Bei einem über mehrere Stunden konstant gehaltenem minimalen Niveau des Blut‐Kortisol‐Spiegels wurde eine maximale Nettobilanz von Aminosäuren beobachtet.Daraus wird gefolgert, daß die periphere Nettobilanz der gesamten Aminosäuren nicht ausschließlich durch den arteriellen Vorrat dieser Nährstoffe gesteuert wird, sondern auch durch einen oder mehrere diurnale Faktoren, von denen einer das Kortisol sein könnte.

Fluxes of haemolymph ammonia and free amino acids in Mytilus edulis exposed to ammonia

Fluxes of haemolymph ammonia and free amino acids in Mytilus edulis exposed to ammonia