Application of in vivo microdialysis to measure leptin concentrations in adipose tissue

Microdialysis is a relatively new in vivo sampling technique, which allows repeated collecting of interstitial fluid and infusion of effector molecules into the tissue without influencing whole body function. The possibility of using microdialysis catheter with a large-pore size dialysis membrane (100 kDa) to measure concentrations of the adipocyte-derived peptide hormone leptin in interstitial fluid of adipose tissue was explored. Krebs–Henseleit buffer with 40 g/l dextran-70 was used to prevent perfusion fluid loss across the dialysis membrane. The relative recovery of leptin in vitro was determined using CMA/65 microdialysis catheter (100 kDa cut-off, membrane length 30 mm; CMA, Stockholm, Sweden) and four perfusion rates were tested (0.5, 1.0, 2.0, 5.0 μl/min). Furthermore, the microdialysis catheter CMA/65 was inserted into subcutaneous abdominal adipose tissue of 11 healthy human subjects and leptin concentrations in the interstitial fluid of adipose tissue in vivo were measured. The present findings are the first documentation on the use of microdialysis to study local leptin concentrations in the interstitial fluid of adipose tissue.     

Impact of separating amino acids between plasma, extracellular and intracellular compartments on estimating protein synthesis in rodents

Summary. Three models representing different separations of amino acid sources were used to simulate experimental specific radioactivity data and to predict protein fractional synthesis rate (FSR). Data were from a pulse dose of ¹⁴C-U Leu given to a non-growing 20 g mouse and a flooding dose of ³H Phe given to a non-growing 200 g rat. Protein synthesis rates estimated using the combined extracellular and intracellular (Ec + Ic) source pool and extracellular and plasma (Ec + Pls) source pool mouse models were 78 and 120% d⁻¹ in liver, 14 and 16% d⁻¹ in brain and 15 and 14% d⁻¹ in muscle. Predicted protein synthesis rates using the Ec + Ic, Ec + Ic + Tr (combined extracellular, intracellular and aminoacyl tRNA source pool) and Ec + Pls rat models were 57, 3.4 and 57% d⁻¹ in gastrocnemius, 58, 71 and 62% d⁻¹ in gut, 8.3, 8.4 and 7.9% d⁻¹ in heart, 32, 23 and 25% d⁻¹ in kidney, 160, 90 and 80% d⁻¹ in liver, 57, 5.5 and 57% d⁻¹ in soleus and 56, 3.4 and 57% d⁻¹ in tibialis. The Ec + Ic + Tr model underestimated protein synthesis rates in mouse tissues (5.0, 27 and 2.5% d⁻¹ for brain, liver and muscle) and rat muscles (3.4, 5.5 and 3.4% d⁻¹ for gastrocnemius, soleus and tibialis). The Ec + Pls model predicted the mouse pulse dose data best and the Ec + Ic model predicted the rat flooding dose data best. Model predictions of FSR imply that identification and separation of the source specific radioactivity is critical to accurately estimate FSR. Received June 11, 2000 Accepted September 26, 2000     

Use of fuzzy clustering technique and matrices to classify amino acids and its impact to Chou's pseudo amino acid composition

In this paper we present a study of classification of the 20 amino acids via a fuzzy clustering technique. In order to calculate distances among the various elements we employ two different distance functions: the Minkowski distance function and the NTV metric. In the clustering procedure we take into account several physical properties of the amino acids. We examine the effect of the number and nature of properties taken into account to the clustering procedure as a function of the degree of similarity and the distance function used. It turns out that one should use the properties that determine in the more important way the behavior of the amino acids and that the use of the appropriate metric can help in defining the separation into groups.     

Serum amino acid concentrations in aging men and women

The age and gender related differences in serum amino acid concentrations have been assessed in 72 (23-92 years) medically screened healthy men and women who were divided into three male and three female groups according to age. Free-time physical activity and food intake were analysed from the 5-day diaries. The subjects were instructed to eat according to their normal dietary habits and to avoid any clinical complementary nutritional products or other products that could increase protein or energy intake. The blood samples (5 ml) taken from the antecubital vein after an over-night fast were analysed for their amino acid contents by chromatography. In total nutrient intake of energy (P < 0.001), protein (P < 0.001), alcohol (P < 0.05), water (P < 0.01), sodium (P < 0.001) and fiber P < 0.001) decreased significantly with age. The concentration of total amino acids (P < 0.01), essential amino acids (P < 0.001), non-essential amino acids (P < 0.05) and branched-chain amino acids (P < 0.05) decreased, whereas citrulline (P < 0.001) and cysteine (P < 0.001) were the only amino acids, which increased with aging. In addition, men had significantly higher concentrations than women of essential amino acids (P < 0.001), branched-chain amino acids (P < 0.001), and 10 of the 22 individual amino acids assayed (P < 0.01). Women had significantly higher concentrations of aspartate (P < 0.05), glycine (P < 0.01), serine (P < 0.001) and taurine (P < 0.01) than men. It is concluded that the decrease in serum total amino acid concentration is associated with decreased energy and protein intake with aging and men have higher essential amino acid concentration in serum than women.     

Effect of the methodology on peptide amino acid concentrations in blood and plasma of sheep

Different methodologies for the measurement of peptide amino acid (PAA) in blood and plasma were compared in sheep. Preparation of blood and plasma samples consisted of a deproteinization, either chemical with sulfosalicylic acid (0.04 g for 1 ml of sample) or physical by ultrafiltration (10,000‐MW cut‐off filters), with or without a subsequent ultrafiltration through a 3,000‐MW cut‐off filter. Peptide concentrations were determined by quantification of amino acid concentrations before and after acid hydrolysis of samples. Free amino acid concentrations were similar by all the method used (about 2.5 and 2.7mM, for blood and plasma respectively). Peptide concentrations were higher with chemical deproteinization (10.6 and 4.2 mM, for blood and plasma respectively) than with physical deproteinization (5.7 and 3.3 mM, for blood and plasma respectively). When the deproteinized samples were further treated to remove material of molecular weight above than 3 kDa, peptide concentrations were significantly reduced, which indicates inefficiencies in the ability of the deproteinizing procedures in removing all the proteinaceous materials. Concentration of small PAA (< 3kDa) in blood was about 1.5‐fold that in plasma, mainly due to peptide Gly and Glu derived from the hydrolysis of the erythrocyte glutathione. The choice of a methodology for quantifying circulating peptides is discussed.     

Indispensable amino acid concentrations decrease in tissues of stomachless fish,common carp in response to free amino acid- or peptide-based diets

Summary. The premise that free amino acid or dipeptide based diets will resolve the nutritional inadequacy of formulated feeds for larval and juvenile fish and improve utilization of nitrogen in comparison to protein-based diets was tested in stomachless fish, common carp (Cyprinus carpio L.) larvae. We examined the postprandial whole body free amino acid (FAA) pool in fish that were offered a FAA mixture based diet for the duration of 2 or 4 weeks. We found that the total amount and all indispensable amino acids concentrations in the whole body decreased after a meal. We then fed juvenile carp with dietary amino acids provided in the FAA, dipeptide (PP), or protein (live feed organisms; brine shrimp Artemia salina nauplii, AS) forms. Histidine concentrations in the whole fish body increased in all dietary groups after feeding whereas all other indispensable amino acids decreased in FAA and PP groups in comparison to the AS group. Taurine appears to be the major osmotic pressure balancing free amino acid in larval freshwater fish which may indicate a conditional requirement. We present the first evidence in larval fish that in response to synthetic FAA and PP diets, the whole body indispensable free AA concentrations decreased after feeding. This study shows that amino acids given entirely as FAA or PP cannot sustain stomachless larval fish growth, and may result in depletion of body indispensable AA and most of dispensable AA. The understanding of these responses will determine necessary changes in diet formulations that prevent accelerated excretion of amino acids without protein synthesis.     

The amino acid composition of tissue protein is affected by the total sulfur amino acid supply in growing pigs

The factorial approach to assess the amino acid (AA) requirements of pigs is based on the assumption that the AA composition of body protein is constant. However, there are indications that this assumption may not be valid because the AA composition of body protein can be affected by the AA supply. The extent to which different tissues are affected by an AA deficiency is unknown. The objective of this study was to investigate the effect of feeding pig diets with a deficient or sufficient total sulfur AA supply (TSAA; Met+Cys) from 6 to 23 weeks of age on tissue composition and meat quality. The deficient diet (TSAA–) provided 24% Met : Lys and 51% TSAA : Lys on a standardized ileal digestible basis, which are 19% and 16% below the recommended requirements, respectively. The sufficient diet (TSAA+) provided 33% Met : Lys and 60% TSAA : Lys. Diets were offered slightly below the ad libitum feed intake capacity of the pigs. Pigs offered diet TSAA– had a lower average daily gain, lower weights of the longissimus dorsi (LM) and rhomboideus muscles (RM), and of selected skin sections (P<0.05). The weight of different sections of the small intestine and the liver was not affected by the diet. The protein content of the LM and RM decreased in pigs offered diet TSAA– (P<0.05), whereas the protein content of other tissues was not affected. The TSAA supply affected the AA composition (g/16 g N) of protein in all tissues, but the Met content was changed only in the liver (P<0.05). Pigs receiving diet TSAA– had a lower Cys content in the RM and in the distal jejunum and ileum (P<0.01). The deficient TSAA supply resulted in a lower carcass weight and higher muscle glycogen stores (P<0.05), but did not affect other meat quality traits. The results of this study indicate that the muscles, jejunum and ileum respond more to a prolonged AA deficiency than the liver. In addition, the observed changes in AA composition of tissue protein question the use of a constant AA profile of retained protein to assess AA requirements.     

Importance of direct determination of amino acid co- and counter-transport stoichiometries

Summary. The stoichiometry of amino acid transport with co- or counter-substrates of a given system has been found to vary with the amino acid species. This phenomenon has been studied directly in only a few cases, however, by measuring the fluxes of the substrates simultaneously. More frequently, the apparent transport stoichiometries of single amino acid species with co- or counter-substrates are estimated indirectly by thermodynamic criteria or cooperative kinetic effects. Unfortunately the latter indirect mea-sures of apparent stoichiometry often yield different results than direct measurement of simultaneous fluxes. These differences often cannot be explained by uncoupled transport of one of the co- or counter-substrates or by other characteristics of the transport process that would make the direct measurement of stoichiometry inaccurate. For these reasons, investigators are encouraged to measure the stoichiometry of transport directly by measuring simultaneous fluxes of co- and counter-substrates. Indirect measures of apparent stoichiometry may, however, reflect important details of a transport mechanism even if they are inconsistent with the actual stoichiometry of transport. Received February 20, 2000 Accepted May 18, 2000     

Co-variation of plasma sodium,taurine and other amino acid levels in critical illness

Summary.  This study investigates the relationship between changes in plasma sodium and changes in amino acid levels in a patient with post-traumatic sepsis and prolonged critical illness. Ninety-two consecutive measurements were performed at regular intervals over a period of many weeks; these consisted in the determination of full amino-acidograms, plasma sodium and complementary variables. A unique, highly significant inverse correlation between taurine and plasma sodium was found (r² = 0.48, p < 0.001). All other amino acids were unrelated, or much more weakly related, to sodium. Taurine was also strongly and directly related to phosphoethanolamine, glutamate and aspartate. Changes in sodium and in levels of these amino acids explained up to 86% of the variability of taurine. Besides, levels of these amino acids maintained a high degree of co-variation, remaining reciprocally related one to each other, directly, with r² ranging between 0.33 and 0.59 (p < 0.001 for all). There were similar findings for β-alanine, which however was measured inconsistently. These data provide gross clinical evidence of a specific link binding plasma sodium and taurine levels, and may be consistent with occurrence of opposite and interdependent shifts of sodium and taurine between intravascular and extravascular space, to maintain osmoregulation. Co-variation of taurine with the other amino acids may be related to the same phenomenon, and/or to similarities in transport systems and chemical structure, or true metabolic interactions. Received April 16, 2002 Accepted June 19, 2002 Published online November 14, 2002 RID="*" ID="*"  Presented at the 7^th International Congress on Amino Acids and Proteins, Vienna (Austria), August 6–10, 2001. Acknowledgements The authors acknowledge the kind assistance of Mr. Maurizio Cianfanelli, from the Catholic University School of Medicine, Rome, Italy. Authors' address: Dr. Carlo Chiarla, Via Augusto Tebaldi, 19, I-00168 Roma, Italy, E-mail: carlo.chiarla@rm.unicatt.it     

Determination of amino acid pairs sensitive to variants in human copper-transporting ATPase 2

In this study, we use our probabilistic approach to analyze the amino acid pairs in human copper-transporting ATPase 2 (ATP7B) in order to determine which amino acid pairs are more sensitive to 125 variants from missense mutant human ATP7B. The results show 97.6% of 125 variants occur at randomly unpredictable amino acid pairs, which account for 80.9% of amino acid pairs in ATP7B, and the chance of occurring of variant is about 9 times higher in randomly unpredictable amino acid pairs than in predictable pairs. Thus, the randomly unpredictable amino acid pairs are more sensitive to variants in human ATP7B.     

Recognition of specific patterns of amino acid inhibition of growth in higher plants, uncomplicated by glutamine-reversible `general amino acid inhibition''

The complexity of the regulatory mechanisms that govern amino acid biosynthesis, particularly in multibranched pathways, frequently results in sensitivity to growth inhibition by exogenous amino acids. Usually the inhibition caused by a given amino acid(s) is relieved by another amino acid(s), thus indicating the cause of inhibition to be a specific interference with endogenous formation of the latter amino acid(s). We recently summarized the evidence that Nicotiana silvestris (and probably most higher plants), in suspension culture, exhibits a separate phenomenon of amino acid mediated growth inhibition called general amino acid inhibition. Every amino acid provokes general amino acid inhibition except for

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-glutamine. In fact,

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-glutamine completely overcomes general amino acid inhibition. We have now demonstrated that specific amino acid inhibition can be recognized and characterized at the level of growth inhibition without interference caused by general amino acid inhibition by the simple provision of exogenous

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-glutamine. Several examples of specific amino acid inhibition of growth were demonstrated in N. silvestris. In one case,

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-threonine inhibits growth partially in the presence of

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-glutamine. The residual amino acid inhibition was overcome by the additional presence of

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-lysine and

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-methionine, indicating that exogenous

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-threonine specifically inhibits the biosynthesis of both

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-lysine and

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-methionine. As a second example, the

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-valine-mediated inhibition of growth that persisted in the presence of

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-glutamine was overcome by

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-isoleucine, indicating that exogenous

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-valine inhibits

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-isoleucine biosynthesis. The use of amino acid analogs as experimental tools for biochemical-genetic studies in higher plants is also complicated by general amino acid inhibition. Conditions were demonstrated under which p-fluorophenylalanine and m-fluorotyrosine could be used as specific antimetabolites of

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-phenylalanine and

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-tyrosine biosynthesis without interference from general amino acid inhibition. We thus present a rigorous basis for recognition of specific relationships between metabolic branches that can guide detailed enzymological analyses.     

Seasonal patterns of nucleic acid concentrations and amino acid profiles of Parapenaeus longirostris (Crustacea, Decapoda): relation to growth and nutritional condition

The present work describes the seasonal changes in nucleic acid concentrations and amino acid profiles in the muscle of juvenile Parapenaeus longirostris and their relation to growth and nutritional condition. RNA content varied significantly between seasons, being the highest values attained in spring and the lowest in winter (p < 0.05). Similar results were obtained with RNA:protein and RNA:DNA ratios. In respect to total amino acid content (TAA), a significant increase from winter to spring was observed (p < 0.05) and the major essential amino acids (EAA) were arginine, histidine and leucine. Within non-essential amino acids (NEAA) glutamic acid, aspartic acid, glycine and proline were dominant. From winter to spring, a significant variation in NEAA content occurred (26.8; p < 0.05), mainly due to the significant increase of glutamic acid (79.1) and serine (66.7) (p < 0.05). EAA content did not vary significantly between seasons (p > 0.05). In opposition, during this period a significant decrease in the free amino acid content (FAA) was observed (p < 0.05); a higher percentage of decrease was attained in free non-essential (FNEAA – 42.9) in comparison to free essential amino acids (FEAA – 40.2). The significant increase in RNA and TAA contents from winter to spring may be related with protein synthesis. On the other hand, the lowest values obtained in winter may be due to a reduction in feeding activity; in this period the muscle protein must be progressively hydrolysed, which is evident with the higher FAA content. The liberated amino acids enter FAA pool and become available for energy production. In conclusion, it was evident that the seasonal cycle in activities such as feeding and growth with nucleic acids and amino acid analyses was noticed.     

Synthesis,evaluation and molecular docking studies of amino acid derived N-glycoconjugates as antibacterial agents

Six amino acid derived N-glycoconjugates of d-glucose were synthesized, characterized and tested for antibacterial activity against G(+)ve (Bacillus cereus) as well as G(−)ve (Escherichia coli and Klebsiella pneumoniae) bacterial strains. All the tested compounds exhibited moderate to good antibacterial activity against these bacterial strains. The results were compared with the antibacterial activity of standard drug Chloramphenicol, where results of A5 (Tryptophan derived glycoconjugates) against E. coli and A4 (Isoleucine derived glycoconjugates) against K. pneumoniae bacterial strains are comparable with the standard drug molecule. In silico docking studies were also performed in order to understand the mode of action and binding interactions of these molecules. The docking studies revealed that, occupation of compound A5 at the ATP binding site of subunit GyrB (DNA gyrase, PDB ID: 3TTZ) via hydrophobic and hydrogen bonding interactions may be the reason for its significant in vitro antibacterial activity.     

Neuronal dependence of extracellular dopamine,acetylcholine, glutamate,aspartate and gamma-aminobutyric acid (GABA) measured simultaneously from rat neostriatum using in vivo microdialysis: reciprocal interactions

Summary The neuronal origin of extracellular levels of dopamine (DA), acetylcholine (ACh), glutamate (Glu), aspartate (Asp) and gamma-aminobutyric acid (GABA) simultaneously collected from the neostriatum of halothane anaesthetized rats with in vivo microdialysis was studied. The following criteria were applied (1) sensitivity to K⁺-depolarization; (2) sensitivity to inhibition of synaptic inactivation mechanisms; (3) sensitivity to extracellular Ca²⁺; (4) neuroanatomical regionality; sensitivity to selective lesions and (5) sensitivity to chemical stimulation of the characterized pathways.It was found that: (1) Extracellular DA levels found in perfusates collected from the neostriatum fulfills all the above criteria and therefore the changes in extracellular DA levels measured with microdialysis reflect actual release from functionally active nerve terminals, and so reflect ongoing synaptic transmission. (2) Changes in neostriatal ACh levels reflect neuronal activity, provided that a ACh-esterase inhibitor is present in the perfusion medium. (3) Extracellular Glu, Asp and GABA could be measured in different perfusion media in the rat neostriatum and probably reflect metabolic as well as synaptic release. However, (4) the majority of the extracellular GABA levels found in perfusates collected from the neostriatum may reflect neuronal release, since GABA levels were increased, in a Ca²⁺-dependent manner, by K⁺-depolarization, and could be selectively decreased by an intrinsic neostriatal lesion. (5) It was not possible to clearly distinguish between the neuronal and the metabolic pools of Glu and Asp, since neostriatal Glu and Asp levels were only slightly increased by K⁺-depolarization, and no changes were seen after decortication. A blocker of Glu re-uptake, DHKA, had to be included in the perfusion medium in order to monitor the effect of K⁺-depolarization on Glu and Asp levels. Under this condition, it was found (6) that neostriatal Glu and Asp levels were significantly increased by K⁺-depolarization, although only increases in the Glu levels were sensitive to Ca²⁺ in the perfusion medium, suggesting that Glu but not Asp is released from vesicular pools. (7) Evidence is provided that selective stimulations of nigral DA cell bodies may lead to changes in release patterns from DA terminals in the ipsilateral neostriatum, which are in turn followed by discrete changes in extracellular levels of GABA and Glu in the same region. Finally, some methodological considerations are presented to clarify the contribution of neuronal release to extracellular levels of amino acid neurotransmitters in the rat neostriatum.     

Feeding and arginine deficient diets differentially alter free amino acid concentrations of hindlimb muscle in young rats

Summary The objective of these experiments was to examine short- and long-term (7 d) effects of arginine-deficient diets on free amino acid concentrations in hindlimb muscle of rats. In rats fed the control diet containing arginine (+Arg), muscle alanine and methionine concentrations were higher 1 and 2h after feeding compared to food-deprived rats, whereas branched-chain amino acids, arginine and asparagine concentrations were lower postprandially. In Experiment 1, rats were fed an arginine-deficient (–Arg) diet with glutamate (+Glu) substituted for arginine; alanine (+Ala), ornithine (+Orn) or citrulline (+Cit) were substituted for arginine in Experiment 2. In Experiment 1, arginine concentrations decreased in blood but not in muscle. This contrasts with rats fed –Arg/+Ala or –Arg/+Orn diets which had muscle arginine concentrations less than half the concentrations in controls or in rats fed the –Arg/+Cit diet. Muscle essential amino acids in Experiment 2 did not differ by diet, but muscle branched-chain amino acids were elevated relative to controls in the rats fed –Arg/+Ala or –Arg/+Orn diets; however, rats fed the –Arg/+Cit diet had levels similar to the controls. Also, muscle branched-chain amino acids were correlated with glutamine concentrations in both blood and muscle. The measurements in the post-meal period suggest that muscle amino acid concentrations may more closely reflect dietary amino acid patterns than do blood amino concentrations.Abbreviations BCAA branched-chain amino acids - BCKADH branched-chain ketoacid dehydrogenase - EAA essential amino acids - LNAA large neutral amino acids - NEAA nonessential amino acids - PDV portal-drained viscera - SELSM standard error of least squares means - SSA 5-sulfosalicylic acid - TAA total amino acids Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.     

A study on the estimation of sulfur-containing amino acid metabolism by the determination of urinary sulfate and taurine

Summary.  Sulfate and taurine are major end products of sulfur-containing amino acid metabolism in mammals including humans, and they are excreted in urine. Average excretions (μmol/mg of creatinine) in the morning urine of 58 female college students were: total (free plus ester) sulfate (a), 12.53 ± 3.85; free sulfate, 11.57 ± 3.69; taurine, 0.78 ± 0.53. Ratio of total sulfate and taurine was 10 : 0.6. Regression lines obtained by plotting total sulfate, free sulfate, or total sulfate plus taurine against urea have shown that the former excretions are significantly correlated with urea excretion. Excretion of total sulfate at zero point of urea excretion (b) was 5.30, which corresponded to 42.3% of average excretion (12.53) and was assumed to be derived from dietary sulfate. The difference 7.23 (a − b) seemed to be derived from sulfur-containing amino acids. It was pointed out that the difference of average sulfate excretion and sulfate excretion at zero urea excretion, namely a − b, was appropriate for the metabolic index of sulfur-containing amino acids of the group examined. As free sulfate constituted 92.3% of total sulfate, excretion of ester sulfate was at a constant level, and that of taurine was not significantly correlated with urea excretion, the value of free sulfate corresponding to the value a − b of total sulfate mentioned above seemed to be a reliable and convenient index in the assessment of sulfur-containing amino acid metabolism. Received December 3, 2001 Accepted January 2, 2002 Published online August 30, 2002 Authors' address: Dr. Toshihiko Ubuka, Department of Clinical Nutrition, Kawasaki University of Medical Welfare, Kurashiki Okayama, 701-0193 Japan, E-mail: ubukatos@mw.kawasaki-m.ac.jp     

Effects of total gastrectomy on plasma silicon and amino acid concentrations in men

The aim of the study was to determine one-year effects of total gastrectomy on plasma silicon and free amino acid concentrations in patients and evaluate changes of volumetric bone mineral density (vBMD) in lumbar spine. Eight patients were enrolled to the control (CTR) group. Six patients subjected to total gastrectomy (GX group) were included to the experimental group. vBMD in trabecular and cortical bone was measured in lumbar vertebrae at baseline (before surgery) and one year later using quantitative computed tomography. Plasma concentrations of silicon and free amino acids were determined at baseline and one year later using photometric method and ion-exchange chromatography. Body weights within CTR and GX groups were not different after one-year follow-up when compared to the baseline values (P > 0.05). An average annual decrease of vBMD in the trabecular bone in the gastrectomized patients reached 15.0% in lumbar spine and was significantly different in comparison to the percentage changes observed in CTR group (P = 0.02). One-year percentage change of vBMD in the cortical bone in L₁ and L₂ has shown significantly decreased values by 10.5 and 9.1% in the GX group when compared to the percentage change observed in the controls (P < 0.05). Plasma concentration of adipic acid was significantly higher by 101.6% one year after total gastrectomy procedure in the patients when compared to the baseline value (P = 0.01). Plasma concentration of silicon was significantly lowered by 26.7% one year after the total gastrectomy when compared to the baseline value (P = 0.009). Total gastrectomy in patients has induced severe osteoporotic changes in lumbar spine within one-year period. The observed osteoporotic changes were associated with decreased plasma concentration of silicon indicating importance of exocrine and endocrine functions of stomach for silicon homeostasis maintenance. Gastrectomy-induced bone loss was not related to decreased amino acid concentration in plasma obtained from overnight fasted patients.     

The effect of heat shock on amino acid transport and cell volume in 3T3 cells

Summary. In 3T3 cells temperatures higher than physiological stimulated amino acid transport activity in a dose-dependent manner up to 44°C. However, the temperature increase did not induce widespread transport increase of all other nutrients tested. The activities of both amino acid transport systems A and ASC were enhanced within a few minutes following cell exposure to increased temperature. The maintenance of this effect required continuous exposure of the cells to hyperthermia. Kinetic analysis indicated that the stimulation of the activity of transport System A occurred through a mechanism affecting Vmax rather than Km. The continuous presence of cycloheximide did not prevent the transport changes induced by hyperthermia. These results suggest that the increased amino acid uptake reflects an activation or relocation of existing amino acid transport proteins. During the hyperthermic treatment, the content of ninhydrin-positive substances (NPS), mostly amino acids, increased within the cells and the accumulation of these compatible osmolytes was parallelled by an increase in cell volume. The withdrawal of amino acids from the culture medium immediately before and during the shock phase counteracted the increase and reduced the NPS content but did not prevent the increase in amino acid transport, the cell swelling and the induction of the heat shock response. Received June 30, 1999 Accepted July 27, 2000