谷氨酰胺在危重病患者中的应用

目的探讨危重病患者中早期经静脉应用谷氨酰胺（glutamine，Gl）的临床价值。方法42例患者随机分成两组（对照组和Gln组），Gln组进行Gln治疗（100mL／d，共7d）。治疗前后检测患者体质量、白蛋白、谷胱甘肽（GSH）、握力的变化和肠功能不全的发生率。结果体质量两组治疗前后比较差异无显著性（P〉0．05）。白蛋白、握力和GSH Gl治疗后非常显著高于治疗前（P〈0．01）；白蛋白对照组治疗后较治疗前显著增高（P〈0．05），但握力和GSH治疗前后均无显著变化（P〉0.05）；肠功能不全的发生率Gln组为4．8％，显著低于对照组（28．6％，P〈0．05）。结论在危重病患者疾病早期通过静脉途径外源性地补充Gln，有效改善了患者的营养状况；使患者血浆中的GSH水平增高，加强了机体的抗氧化能力；减少了患者肠功能不全的发生率。     

口服谷氨酰胺颗粒对烧创伤患者的疗效及安全性分析

目的观察口服谷氨酰胺(Gln)颗粒对烧(创)伤及大手术患者的疗效及可能发生的不良反应.方法采用随机双盲、安慰剂对照法,将受试患者分为Gln组和对照组,每组60例,两组患者采用等氮、等热量的营养支持.Gln组口服或管饲Gln 0.5 g·kg-1·d-1,对照组使用同等剂量的安慰剂甘氨酸,疗程均为7 d.比较用药前后两组患者肠黏膜屏障功能、蛋白代谢、免疫功能、肝和肾功能的变化及不良反应等. 结果伤后两组患者血浆Gln浓度明显低于正常值,而血浆二胺氧化酶(DAO)活性、内毒素含量、肠黏膜通透性[尿乳果糖/甘露醇(L/M)]及尿氮排量均明显增高;但Gln组用药7 d后血浆Gln浓度与用药前比较增加38.04%(P＜0.01).Gln组血浆前白蛋白、转铁蛋白及白细胞介素2(IL-2)含量均显著高于对照组(P＜0.01),升幅分别为21.19%、51.11%、57.54%.血浆DAO活性、L/M比值、内毒素含量及尿氮排量明显低于对照组,降幅分别为47.26%、52.18%、22.22%、27.78%(P＜0.05或0.01).两组患者的血浆总蛋白、白蛋白、血尿常规及肝、肾功能在用约前后变化不明显(P＞0.05).用药后有少数患者出现轻微不良反应如恶心、腹泻和便秘等,2～3 d后自行缓解,两组间比较,差异无显著性意义(P＞0.05).结论口服Gln能显著提高患者血浆Gln浓度,明显减轻伤后肠黏膜受损程度,并能促进机体蛋白合成,降低蛋白分解,提高机体免疫功能,且临床应用无明显不良反应.     

Reversible shifts in the Ca2+-dependent release of aspartate and glutamate from hippocampal slices with changing glucose concentrations

It is known that low glucose concentrations increase the aspartate and decrease the glutamate content of brain tissue both in vivo and in vitro. To see whether these changes occur in the transmitter compartment or not, the release of aspartate and glutamate evoked by electrical-field stimulation or by high K+ was followed in slices of rat hippocampus superfused with 5 or 0.2 mM glucose. Superfusion with 0.2 mM glucose increased the evoked release of aspartate about ten times and that of glutamate about threefold. This shift in the ratio of aspartate to glutamate released was accompanied by a similar increase in the relative amount of aspartate contained in the slices. The high evoked release of aspartate and glutamate was well maintained, provided 0.5 mM glutamine was added to the medium. Changing the concentration of glucose after the first period of stimulation rapidly altered the relative amounts of aspartate and glutamate released but not the enhanced release of glutamate. The large evoked release of both aspartate and glutamate in 0.2 mM glucose was almost entirely Ca2+-dependent. The relative amounts of aspartate and glutamate released by 50 mM K+ also changed when the glucose concentration was reduced. Results suggest two effects of low glucose concentrations: an increase in the overflow of synaptically released glutamate due to a decreased uptake and an increase in the proportion of aspartate to glutamate formed and released from the transmitter pool. These observations are consistent with the interpretation that these two transmitters can be released in different proportions from the same terminals.     

Glutamine and Other Amino Acid Losses During Continuous Venovenous Hemodiafiltration

Abstract: Serum amino grams and daily losses of glutamine (Gin) and other amino acids (AAs) into diafiltrate were measured during the first 5 days of continuous venovenous hemodiafiltration (CVVHDF) in 6 ICU patients with acute renal failure (ARF). Four patients had ARF as a part of multiple organ failure (MOF) of septic origin, and 2 patients had isolated ARF because of primary renal disease. During the study, all the patients received defined total parenteral nutrition (TPN). The mean daily AA losses into dialysate were relatively low (0.61 ± 0.1 g N ) and reached 4.5% of the daily AA substitution. Gln represented 32.7 ± 5.9% of the total AA losses (0.19 ± 0.04 g N ). Serum levels of Gin (p = 0.002) and of most other AAs were significantly lower in the patients than in the control subjects (AA analysis in 16 healthy volunteers). Phenylalanine (Phe) was the only AA that was increased significantly (p < 0.01) in the patients. The mean patient serum concentrations of Phe and tyrosine were significantly higher (p < 0.03) than the correspondent concentrations in dialysate, but the lysine concentration was higher in dialysate (p < 0.03). The serum and dialysate concentrations of other AAs did not differ. Gin in serum decreased significantly (p < 0.03) on the second day of CVVHDF but returned to the baseline levels subsequently. Serum concentrations of Phe increased on the second day of CVVHDF (p < 0.05). Serum concentrations of other AAs remained stable during the whole study. We conclude that Gin losses into dialysate during CVVHDF are relatively low, but CVVHDF itself may induce changes in Gin metabolism and distribution that are reflected by a decrease of serum Gin levels at the institution of this treatment. Therefore, the need for Gin supplementation in ICU patients is even greater in the first days of CVVHDF.     

Isolation of a DNA fragment which complements glutamine synthetase deficient strains ofS. pombe

Summary From a gene bank ofS. pombe DNA, a 5.6 kb clone was isolated which complemented mutants defective in glutamine synthetase (GS) activity. Sub-cloning fragments of this 5.6 kb clone showed that the complementing activity was localised in a 1.6 kb HindIII-Aval fragment and a partial DNA sequence revealed an open reading frame preceded by TATA sequences and a TGACTA sequence. Plasmid constructs carrying up to 3.4 kb of DNA used to transformgln ⁻ strains gave transformants which showed a wide range of GS activity, in some cases 100 times the wild-type level. These constructs identify DNA sequences lying downstream from the putative coding sequence which have effects on the total amount of enzyme activity, but do not affect the control imposed by the nitrogen source on which the cells are grown.     

The hyperpolarisation-activated current,I f,is not required for pacemaking in single cells from the rabbit atrioventricular node

Using electrophysiological and radiotracer studies in parallel, we have investigated the characteristics of the endogenous Na⁺-dependent amino acid transporter (system B^0,+) in Xenopus oocytes with regard to ion dependence, voltage dependence and transport stoichiometry. In voltage-clamped oocytes (–60 mV) superfusion with saturating concentrations of amino acids (1 mM) in 100 mM NaCl resulted in reversible, inward currents (mean±SEM): alanine, 1.83±0.09 nA (n=21); arginine, 2.54±0.18 nA (n=17); glutamine, 1.73±0.10 nA (n=19). Only arginine evoked a current in choline medium (0.50±0.13 nA, n=10), whereas Cl^– replacement had no effect on evoked currents. The glutamine-evoked current was saturable (I _max=1.73 nA, glutamine K _m=0.12 mM) and linearly dependent upon voltage between –90 and –30 mV. Using direct and indirect (activation) methods, we found that transport can proceed with Na⁺/amino acid coupling stoichiometry of either 11 or 21, but coupling was the same for each amino acid tested (alanine, arginine and glutamine) within a batch of oocytes (i.e. from a single toad). Despite the net single positive charge on arginine, the magnitude of the net transmembrane charge movement during Na⁺-coupled arginine transport was identical to that for the zwitterionic neutral amino acids glutamine and alanine; this may be explained by a concomitant stimulation of K⁺ efflux during arginine transport with a putative coupling of 1 K⁺1 arginine.     

Ischemic disruption of glutamate homeostasis in brain: quantitative immunocytochemical analyses

More than 10 years ago, it was shown by microdialysis that the excitatory transmitter glutamate accumulates in the interstitial space of brain subjected to ischemic insult. This was one of the key observations leading to the formulation of the `glutamate hypothesis' of ischemic cell death. It is now assumed that even a transient glutamate overflow may set in motion a number of events that ultimately cause cell loss in vulnerable neuronal populations. The aim of the present review is to discuss the intracellular changes that underlie the dysregulation of extracellular glutamate during and after ischemia, with emphasis on data obtained by postembedding, electron microscopic immunogold cytochemistry. While the time resolution of this approach is necessarily limited, it can reveal, quantitatively and at a high level of spatial resolution, how the intracellular pools of glutamate and metabolically related amino acids are perturbed during and after an ischemic insult. Moreover, this can be done in animals whose extracellular amino acid levels are monitored by microdialysis, allowing a direct correlation of extra- and intracellular changes. Immunogold analyses of brains subjected to ischemia have identified dendrites and neuronal somata as likely sources of glutamate efflux, probably mediated by reversal of glutamate uptake. The vesicular glutamate pool has been found to be largely unchanged after 20 min of ischemia. Ischemia causes an increased glutamate content and an increased glutamate/glutamine ratio in glial cells, as revealed by double immunogold labelling. This argues against the idea that glial cells contribute to the extracellular overflow of glutamate in the ischemic brain.     

Distribution of glutamine-like immunoreactivity in the cerebellum of rat and baboon (Papio anubis) with reference to the issue of metabolic compartmentation

Summary The cellular and subcellular localization of glutamine, a major glutamate precursor, was studied by means of an antiserum raised against glutaraldehydefixed glutamine. Ultrathin sections from the cerebellar cortex of rat and baboon (Papio anubis) were incubated sequentially in the primary antiserum and in a secondary antibody coupled to colloidal gold particles. The labelling intensity was quantified by computer-aided calculation of gold particle densities. High levels of immunoreactivity occurred in glial cells (Bergmann fibres, astrocytes, and oligodendrocytes), intermediate levels in cell bodies and processes of granule cells, and low levels in terminals of presumed GABAergic or glutamatergic fibres (terminals of basket and Golgi cells, and of parallel, mossy, and climbing fibres). The labelling intensity of Purkinje cells showed some variation, but never exceeded that in glial cells. Within the nerve fibre terminals, the glutamine-like immunoreactivity showed some preference for mitochondria, but was otherwise evenly distributed. The predominant glial localization of glutamine was also obvious in light microscopic preparations processed according to the postembedding peroxidase-antiperoxidase procedure. Gold particle densities over different types of profile in glutamine immunolabelled sections were compared with particle densities over the corresponding types of profiles in neighbouring sections labelled with an antiserum to glutaraldehyde-fixed glutamate. The glutamate/glutamine ratio, expressed arbitrarily by the ratio between the respective gold particle densities, varied by a factor of about 6, with the highest ratio in the putative glutamatergic mossy and parallel fibre terminals, and the lowest ratio in glial elements. The remaining tissue components displayed intermediate ratios. The present study provides direct morphological evidence for the existence in the brain of distinct compartments with differing glutamate/glutamine ratios.This paper is dedicated to Professor Fred Walberg on the occasion of his 70th birthdayOn leave of absence from Department of Anatomy, Capital Institute of Medicine, You An Men Street, Beijing, China     

氟尿嘧啶对大鼠小肠的损伤作用研究

目的：探讨氟尿嘧啶对大鼠小肠的损伤作用,方法：通过胃管连续2d给予大鼠尿嘧啶125mk/kg.d,观察给药后第1天－第7天大鼠每日饮食量的变化,给药前和给药后的第8天分别称大鼠体重,给药后第8天测定门静脉血流量及门静脉压,分析小肠形态学变化,观察小肠对色氨酸吸收能力,测定动脉血谷氨酰胺的浓度,结果：给药后第1天－第7天大鼠饮食量均明显低于正常,尤其是第2天－第4天最为严重,第8天大鼠体重下降,小肠结构有明显损伤,门静脉血流量减少,门静脉压下降,小肠对色氨酸的吸收及动脉血谷氨酸胺浓度明显下降,与对照组相比的均有显著差异,结论：氟尿嘧啶可导致大鼠小肠结构和功能的明显障碍。     

Simultaneous action of MK-801 (dizclopine) on dopamine, glutamate, aspartate and GABA release from striatum isolated nerve endings

The simultaneous effect of MK-801 on the baseline- and depolarization (20 microM veratridine or 30 mM high K+)-evoked release of endogenous dopamine, glutamate (Glu), aspartate (Asp), and GABA is investigated in the same preparation of rat striatum isolated nerve endings. MK-801, in the microM range, selectively increases the baseline and high K+ depolarization-evoked release of dopamine, without causing any effect on the baseline or on the high K+-evoked release of Glu, Asp and GABA. In addition to this selective action on dopamine release, MK-801 inhibits the veratridine depolarization-evoked release of all the neurotransmitters tested, including dopamine. In SBFI and fura-2 preloaded striatal synaptosomes, MK-801 inhibits the elevation of internal Na+ (Na(i)) and the elevation of internal Ca2+ (Ca(i)) induced by veratridine depolarization. The elevation of Ca(i) induced by high K+ depolarization is unchanged by MK-801. This study reveals two separate MK-801 actions. (1) The voltage-independent action, which increases dopamine release selectively, and might contribute to the effects of MK-801 on motor coordination. (2) The voltage-dependent action, which inhibits all the veratridine-evoked responses including the evoked release of the excitatory amino acids (which are particularly concentrated in striatum nerve endings), and might contribute to the anticonvulsant and neuroprotective effects of MK-801.