土壤pH对玉米与微生物竞争吸收氨基酸的影响

化学合成肥料的大量使用导致土壤pH发生显著变化,但其对植物与根际微生物竞争吸收氨基酸的影响机制尚不明确.本试验通过电解法调节杭州红壤和铁岭棕壤两种土壤pH, 采用外源添加¹⁵N标记甘氨酸短期吸收4 h的方法,研究了pH对玉米及根际微生物竞争吸收氨基酸的影响.结果表明:土壤pH对玉米根和地上部生物量有显著影响,对于红壤,pH为6.48最适宜玉米生长,且玉米地上部¹⁵N丰度和¹⁵N-甘氨酸吸收量也显著高于其他处理;对于棕壤,pH为7.65最适宜玉米生长,其玉米地上部和根系¹⁵N丰度显著低于pH为5.78处理,但¹⁵N-甘氨酸吸收量显著高于其他处理.红壤pH为6.48条件下,其微生物生物量碳相对较高,而棕壤pH为7.65条件下,其微生物生物量碳相对较低.综合根系吸收、转运及微生物竞争吸收的结果,推断红壤在pH为6.48条件下虽然面临着微生物的竞争吸收,但生长于其上的玉米通过提高吸收速率和转移比率提高了氨基酸的吸收量;在pH为7.65的棕壤中,微生物活性较低,降低了与玉米竞争吸收氨基酸的能力,从而增加了玉米对氨基酸的吸收量.     

运动和制动大鼠腓肠肌内p-Akt/MuRF1/FoxO1的蛋白表达变化

本文旨在研究两种运动方式和制动状态下大鼠腓肠肌内p-Akt/MuRF1/FoxO1的蛋白表达变化,以揭示运动员不同的训练方式和停训状态下肌形态学改变的分子机制。Sprague Dawley(SD)大鼠随机分成对照组、耐力训练组、后肢悬垂组和离心训练组。耐力训练组接受跑台训练,悬吊组接受后肢悬垂,离心训练组接受坡度-16o的跑台训练。各组大鼠取腓肠肌,称取其重量,HE法测定骨骼肌细胞横截面积;免疫组化法测定p-Akt蛋白表达;免疫印迹法测定MuRF1、FoxO1的蛋白表达。结果显示,相对对照组,耐力训练组腓肠肌重量和细胞横截面积无显著变化,而离心训练组和后肢悬垂组显著降低;耐力训练组和离心训练组腓肠肌p-Akt蛋白表达显著增加,后肢悬垂组无明显变化。与对照组相比,耐力训练组MuRF1蛋白表达无明显变化,而离心训练组和后肢悬垂组则显著升高;耐力训练组FoxO1蛋白表达显著降低,而离心训练组与后肢悬垂组则显著升高。以上结果表明,增加活动的运动方式(耐力和离心训练)激活了Akt表达,但没有引起肌肉重量的增加;相反,离心训练和后肢悬垂均显著增加了MuRF1和FoxO1的蛋白表达,导致肌肉萎缩,提示MuRF1和FoxO1是造成肌肉萎缩的主要决定因素。     

神经营养因子对神经肌肉接头传递的调制作用

运动单位由运动神经元及其支配的肌纤维组成。神经肌肉接头(neuromuscular junction,NMJ)传递受到严密的调节,因而能和运动单位的活动协调一致。在NMJ,神经调制物质的释放与运动单位的活动有关,并能决定突触传递的效能。脑源性神经营养因子(brain—derived neurotrophic factor,BDNF)和神经营养因子4(neurotrophin-4,NT-4)由运动神经末梢和肌纤维产生。肌肉释放营养因子受肌肉活动调节。在NMJ,BDNF和NT-4通过激活酪氨酸激酶B受体(tyrosine kinase receptor B,TrkB),能加强自发性和诱导性的突触活动。突触前Ca^2 量的迅速增加或突触胞吐过程的易化,都能增加突触囊泡的释放,从而改善NMJ的突触传递。事实上,BDNF能促进突触前细胞内Ca^2 的释放,TrkB的激活也能通过有丝分裂活化蛋白激酶,引起突触素I(synapsinI)的磷酸化,进而增加可释放的突触囊泡的数量。在NMJ,神经营养因子还能通过影响神经调节素(neuregulin)或其他神经源性调制物质的局部释放,对接头传递进行调节。本文对近年来在NMJ突触传递的调节,运动单位的NMJ特性以及神经营养因子对突触传递效能的影响等方面的研究进展做一综述。     

软组织扩张下的生物力学特性

对狗后肢扩张后和对照侧的隐神经、隐动脉、隐静脉进行应力－应变、应力松驰实验,确定其应力－应变函数和连续松驰谱的各参数。从应力－应变曲线和归一化连续松驰曲线来看,在扩张后的短时期内,随着扩张器注水量的增加,扩张后样品的力学特性相对于其对照侧样品的特性又趋于接近,隐神经,隐动脉,隐静脉都表现出这样的规律。     

兴奋性氨基酸介导脊髓伤害性信息传递

ＮＭＤＡ和非ＮＭＤＡ受体广泛存在于猫脊髓背角神经元上,并参与介导伤害性信息传递;ＮＭＤＡ受体主要介导皮肤的伤害性传入,非ＮＭＤＡ受体则主要介导肌肉和内脏的伤害性传入;皮肤和肌肉的伤害性传入分别诱发释放更多的门冬氨酸和谷氨酸可能是这种差别的主要原因之一;ＮＭＤＡ受体的不同调节位点在伤害性信息传递中有密切的协同作用;兴奋性氨基酸和Ｐ物质及其受体在介导和调制伤害性信息传递中的相互作用可以分别发生在神经元     

Ghrelin:一种新发现的生长激素释放肽

Ghrelin是一种新发现的含有28个氨基酸的生长激素释放肽,为生长激素促分泌素受体(growthhormonesecretagoguereceptor,GHSR)的内源性配体。当Ghrelin与其特异性受体(GHSR)结合后会产生一系列生物学效应。Ghrelin具有刺激垂体前叶释放生长激素、增加食欲、调节能量代谢平衡,以及促进胃酸分泌等生物学功能,其作用机制目前尚不清楚。     

宁夏枸杞体细胞胚发生过程中对金属离子的吸收速率和游离氨基酸含量的变化

采用多重示踪技术研究宁夏枸杞 (Lyciumbar barumL .)体细胞胚发生中对多种金属离子的吸收动态及其与游离氨基酸含量变化之间的关系。结果表明 :(1)在枸杞体细胞胚发生中对一些金属离子具有选择吸收特性 ,而且在体细胞胚发育不同时期对同一种金属离子的吸收量也不同 ;(2 )在枸杞体细胞胚发生早期对多数金属离子吸收量迅速增加 ,而后下降。到球形胚期吸收量达到第二个峰值 ,而且金属离子被吸收后提高了体细胞胚发生的频率 ;(3)枸杞体细胞胚发生中游离氨基酸总量从胚性细胞启动期开始下降 ,到胚性细胞形成期到达谷底 ,然后开始上升 ,到多细胞原胚期达到峰值 ,多数游离氨基酸含量变化与金属离子被吸收的量相交叉 ;(4 )外加RbCl和SrCl2 对枸杞体细胞胚发生具有促进作用 ,而且加大了几种游离氨基酸含量变化的幅度。文章讨论了它们之间的关系及其可能的作用机理     

棘复蛙肌肉营养成份与能量含量

我们在棘腹蛙能流模型及人工繁殖技术研究中,对其营养成份及含肉率进行了初步研究。 材料 棘腹蛙幼娃和成蛙,均来自湘西的溪流中。 方法 1.将12只活蛙擦干称重后处死,除去皮肤与内脏,然后分成头、躯干、前肢和后肢等部分,并除去非肌肉质后称重,得各部分的肌肉含量。2.用索氏提取法测定脂肪含量,用微量凯氏定氮法测定蛋白质含量。3.用日立835—50型氨基酸分析仪测定肌肉蛋白质的各种氨基酸含量。4.用GR3500-B1微电脑热量计测定肌肉的能量含量。     

肢体负压对犬后肢动脉闭塞病影响的实验研究

目的为研究肢体负压疗法的疗效及探讨其作用机理,我们对犬后肢进行实验研究。方法。实验犬分三组,治疗组为左后肢缺血模型犬并行患者肢负压治疗;对照组同治疗组但不做治疗：自身对照组为双后肢缺血模型犬,左侧行负压治疗,右侧作为对照。     

锌离子：一种内源性的神经调质

锌离子（Zn^2 )广泛存在于中枢神经系统中,其释放呈钙依赖性。近年来,许多证据表明,Zn^2 能调节递质的释放,并调制电压门控通道和配体（兴奋性、抑制性氨基酸）门控通道,表明它是一种重要的内源性神经调质。     

Transport of amino acids in the splanchnic bed by blood plasma and blood in the preruminant calf]

Three preruminant calves were fitted with catheters in portal and hepatic veins and in a mesenteric artery. Two electromagnetic flowmeter probes were clipped around the portal vein and the hepatic artery. The calves were fed either a diet with a low (L) or a high (R) abomasal emptying rate for dietary proteins. Blood flow and free amino acid levels in plasma (P) and blood (S) were determined before the morning meal and during the following 7 h. In the portal vein, for most amino acids P/S ratios were correlated to the net amino acid balance of the digestive tract measured in plasma. By contrast in the hepatic vein, these ratios were mainly correlated to hepatic balance measured in whole blood. Correlations between digestive tract and hepatic balance calculated using either plasma or whole blood pool were different for some amino acids. This suggests that amino acid exchange between plasma and blood cells is low and absorbed amino acids are mainly transported to the liver by plasma, whereas whole blood rather than plasma is concerned in amino acid exchanges in the liver.     

Amino acid repletion does not decrease muscle protein catabolism during hemodialysis

Intradialytic protein catabolism is attributed to loss of amino acids in the dialysate. We investigated the effect of amino acid infusion during hemodialysis (HD) on muscle protein turnover and amino acid transport kinetics by using stable isotopes of phenylalanine, leucine, and lysine in eight patients with end-stage renal disease (ESRD). Subjects were studied at baseline (pre-HD), 2 h of HD without amino acid infusion (HD-O), and 2 h of HD with amino acid infusion (HD+AA). Amino acid depletion during HD-O augmented the outward transport of amino acids from muscle into the vein. Increased delivery of amino acids to the leg during HD+AA facilitated the transport of amino acids from the artery into the intracellular compartment. Increase in muscle protein breakdown was more than the increase in synthesis during HD-O (46.7 vs. 22.3%, P < 0.001). Net balance (nmol.min(-1).100 ml (-1)) was more negative during HD-O compared with pre-HD (-33.7 +/- 1.5 vs. -6.0 +/- 2.3, P < 0.001). Despite an abundant supply of amino acids, the net balance (-16.9 +/- 1.8) did not switch from net release to net uptake. HD+AA induced a proportional increase in muscle protein synthesis and catabolism. Branched chain amino acid catabolism increased significantly from baseline during HD-O and did not decrease during HD+AA. Protein synthesis efficiency, the fraction of amino acid in the intracellular pool that is utilized for muscle protein synthesis decreased from 42.1% pre-HD to 33.7 and 32.6% during HD-O and HD+AA, respectively (P < 0.01). Thus amino acid repletion during HD increased muscle protein synthesis but did not decrease muscle protein breakdown.     

Protein turnover and amino acid transport kinetics in end-stage renal disease

Protein and amino acid metabolism is abnormal in end-stage renal disease (ESRD). Protein turnover is influenced by transmembrane amino acid transport. The effect of ESRD and hemodialysis (HD) on intracellular amino acid transport kinetics is unknown. We studied intracellular amino acid transport kinetics and protein turnover by use of stable isotopes of phenylalanine, leucine, lysine, alanine, and glutamine before and during HD in six ESRD patients. Data obtained from amino acid concentrations and enrichment in the artery, vein, and muscle compartments were used to calculate intracellular amino acid transport and muscle protein synthesis and catabolism. Fractional muscle protein synthesis (FSR) was estimated by the precursor product approach. Despite a significant decrease in the plasma concentrations of amino acids in the artery and vein during HD, the intracellular concentrations remained stable. Outward transport of the amino acids was significantly higher than the inward transport during HD. FSR increased during HD (0.0521 +/- 0.0043 vs. 0.0772 +/- 0.0055%/h, P < 0.01). Results derived from compartmental modeling indicated that both protein synthesis (118.3 +/- 20.6 vs. 146.5 +/- 20.6 nmol.min-1.100 ml leg-1, P < 0.01) and catabolism (119.8 +/- 18.0 vs. 174.0 +/- 14.2 nmol.min-1.100 ml leg-1, P < 0.01) increased during HD. However, the intradialytic increase in catabolism exceeded that of synthesis (57.8 +/- 13.8 vs. 28.0 +/- 8.5%, P < 0.05). Thus HD alters amino acid transport kinetics and increases protein turnover, with net increase in protein catabolism.     

Short-term insulin and nutritional energy provision do not stimulate muscle protein synthesis if blood amino acid availability decreases

Muscle protein synthesis requires energy and amino acids to proceed and can be stimulated by insulin under certain circumstances. We hypothesized that short-term provision of insulin and nutritional energy would stimulate muscle protein synthesis in healthy subjects only if amino acid availability did not decrease. Using stable isotope techniques, we compared the effects on muscle phenylalanine kinetics across the leg of an amino acid-lowering, high-energy (HE, n = 6, 162 +/- 20 kcal/h) hyperglycemic hyperlipidemic hyperinsulinemic clamp with systemic insulin infusion to a low-energy (LE, n = 6, 35 +/- 3 kcal/h, P < 0.05 vs. HE) euglycemic hyperinsulinemic clamp with local insulin infusion in the femoral artery. Basal blood phenylalanine concentrations and phenylalanine net balance, muscle protein breakdown, and synthesis (nmol.min(-1).100 g leg muscle(-1)) were not different between groups. During insulin infusion, femoral insulinemia increased to a similar extent between groups and blood phenylalanine concentration decreased 27 +/- 3% in the HE group but only 9 +/- 2% in the LE group (P < 0.01 HE vs. LE). Phenylalanine net balance increased in both groups, but the change was greater (P < 0.05) in the LE group. Muscle protein breakdown decreased in the HE group (58 +/- 12 to 35 +/- 7 nmol.min(-1).100 g leg muscle(-1)) and did not change in the LE group. Muscle protein synthesis was unchanged in the HE group (39 +/- 6 to 30 +/- 7 nmol.min(-1).100 g leg muscle(-1)) and increased (P < 0.05) in the LE group (41 +/- 9 to 114 +/- 26 nmol.min(-1).100 g leg muscle(-1)). We conclude that amino acid availability is an important factor in the regulation of muscle protein synthesis in response to insulin, as decreased blood amino acid concentrations override the positive effect of insulin on muscle protein synthesis even if excess energy is provided.     

Nitrogen flux across ovine maternal and fetal hindquarters during fasting

Nitrogen flux across the hindquarters of fetal and maternal sheep (n = 15) was determined during normal feeding and following 5 days of maternal fasting. Arterial and venous whole blood concentrations of free amino acids, ammonia and oxygen were measured entering and exiting the hindquarters. Further, the DNA, protein and nitrogen contents of the hindlimb skeletal muscle of the fetus were determined in the fed state and following the 5-day fast. Results of these studies indicate that maternal and fetal hindlimb metabolism differ during fasting. There is a net efflux of alanine, glutamine and total nitrogen from the maternal hindquarters following 5 days of fasting. The fetus also releases glutamine and alanine from the hindquarters during the fast, presumably as potential energy substrate. However, nitrogen balance across the fetal hindquarter remains positive as a result of increased positive arteriovenous differences for other amino acids (particularly leucine and isoleucine). The concentrations of DNA, protein and nitrogen in fetal skeletal muscle remain unchanged during fasting. These data indicate that, whereas the mother undergoes protein catabolism and net nitrogen loss from the hindquarter during fasting, the fetus maintains a positive nitrogen balance across the hindquarter.     

Amino acid metabolism in leg muscle after an endotoxin injection in healthy volunteers

Decreased plasma amino acid concentrations and increased net release of amino acids from skeletal muscle, especially for glutamine, are common features in critically ill patients. A low dose of endotoxin administered to healthy volunteers was used as a human model for the initial phase of sepsis to study the early metabolic response to sepsis. Six healthy male volunteers were studied in the postabsorptive state. Blood samples from the forearm artery and femoral vein were taken during 4 h before and 4 h after an intravenous endotoxin injection (4 ng/kg body wt). In addition, muscle biopsies from the leg muscle were taken. Plasma concentration of the total sum of amino acids decreased by 19% (P = 0.001) and of glutamine by 25% (P = 0.004) the 3rd h after endotoxin administration. At the same time, muscle concentrations of the sum of amino acids and glutamine decreased by 11% (P = 0.05) and 9% (P = 0.09), respectively. In parallel, the efflux from the leg increased by 35% (P = 0.004) for the total sum of amino acids and by 43% (P = 0.05) for glutamine. In conclusion, intravenous endotoxin administration to healthy volunteers, used as a model for the initial phase of sepsis, resulted in a decrease in plasma amino acid concentrations. At the same time, amino acid concentrations in muscle tissue decreased, whereas the efflux of amino acids from leg skeletal muscle increased.     

NOS3 is involved in the increased protein and arginine metabolic response in muscle during early endotoxemia in mice

Sepsis is a severe catabolic condition. The loss of skeletal muscle protein mass is characterized by enhanced release of the amino acids glutamine and arginine, which (in)directly affects interorgan arginine and the related nitric oxide (NO) synthesis. To establish whether changes in muscle amino acid and protein kinetics are regulated by NO synthesized by nitric oxide synthase-2 or -3 (NOS2 or NOS3), we studied C57BL6/J wild-type (WT), NOS2-deficient (NOS2-/-), and NOS3-deficient (NOS3-/-) mice under control (unstimulated) and lipopolysaccharide (LPS)-treated conditions. Muscle amino acid metabolism was studied across the hindquarter by infusing the stable isotopes L-[ring-2H5]phenylalanine, L-[ring-2H2]tyrosine, L-[guanidino-15N2]arginine, and L-[ureido-13C,2H2]citrulline. Muscle blood flow was measured using radioactive p-aminohippuric acid dilution. Under baseline conditions, muscle blood flow was halved in NOS2-/- mice (P < 0.1), with simultaneous reductions in muscle glutamine, glycine, alanine, arginine release and glutamic acid, citrulline, valine, and leucine uptake (P < 0.1). After LPS treatment, (net) muscle protein synthesis increased in WT and NOS2-/- mice [LPS vs. control: 13 +/- 3 vs. 8 +/- 1 (SE) nmol.10 g(-1).min(-1) (WT), 18 +/- 5 vs. 7 +/- 2 nmol.10 g(-1).min(-1) (NOS2-/-); P < 0.05 for LPS vs. control]. This response was absent in NOS3-/- mice (LPS vs. control: 11 +/- 4 vs. 10 +/- 2 nmol.10 g(-1).min(-1)). In agreement, the increase in muscle arginine turnover after LPS was also absent in NOS3-/- mice. In conclusion, disruption of the NOS2 gene compromises muscle glutamine release and muscle blood flow in control mice, but had only minor effects after LPS. NOS3 activity is crucial for the increase in muscle arginine and protein turnover during early endotoxemia.     

克仑特罗对绵羊肝脏血液中IGF-Ⅰ、GH和胰岛素水平的影响

克仑特罗 (ｃｌｅｎｂｕｔｅｒｏｌ ,ＣＬ)为一种 β -肾上腺素能受体激动剂。自 80年代初发现 β -受体激动剂可促进机体生长并改变机体胴体组成以来 ,许多研究均显示 β -激动剂具促进脂肪动员、减少体脂沉积、增加氮素贮存和促进蛋白质合成等作用 ,进而调节机体的生长发育 ,因而 β -激动剂又被称为“营养分重分配剂” (Ｙａｎｇ＆ＭｃＥｌｌｉｇｏｔｔ ,1989;Ｃａｒｄｏｓｏ＆Ｓｔｏｃｋ ,1996;Ｓｍｉｔｈ ,1998)。然而机体内代谢水平在很大程度上受内分泌的调控。在对影响机体生长发育的内分泌研究中 ,越来越多的证据表明胰岛素样生长…     

Nonessential amino acids are not necessary to stimulate net muscle protein synthesis in healthy volunteers

The present study was performed to test the hypothesis that orally administered essential amino acids, in combination with carbohydrate, will stimulate net muscle protein synthesis in resting human muscle in vivo. Four volunteers ingested 500 mL of a solution containing 13.4 g of essential amino acids and 35 g sucrose (EAA). Blood samples were taken from femoral arterial and venous catheters over a 2-hour period following the ingestion of EAA to measure arteriovenous concentrations of amino acids across the muscle. Two muscle biopsies were taken during the study, one before administration of the drink and one approximately 2 hours after consumption of EAA. Serum insulin increased from normal physiologic levels at baseline (9.2 +/- 0.8 microU/mL) and peaked (48 +/- 7.1 microU/mL) 30 minutes after EAA ingestion. Arterial essential amino acid concentrations increased approximately 100 to 400% above basal levels between 10 and 30 minutes following drink ingestion. Net nitrogen (N) balance changed from negative (-495 +/- 128 nmol/mL) prior to consumption of EAA to a peak positive value (416 +/- 140 nmol/mL) within 10 minutes of ingestion of the drink. EAA resulted in an estimated positive net N uptake of 307.3 mg N above basal levels over the 2-hour period. Muscle amino acid concentrations were similar prior to and 2 hours following ingestion of EAA. We conclude that ingestion of a solution composed of carbohydrates to stimulate insulin release and a small amount of essential amino acids to increase amino acid availability for protein synthesis is an effective stimulator of muscle protein anabolism.     

Hind leg muscle amino acid balances in cold-exposed rats

The changes in hind leg tissue (muscle and skin) amono acid pool size and arteriovenous balance were measured in rats subjected to 0–90 min of cold exposure (4°C). Tissue free amino acid pools presented a different composition pattern from protein amino acids. Muscle rapidly reacted to cold exposure by releasing small amounts of some amino acids (alanine, aspartate), with only small changes in pool size during the first 30 min. Amino acid oxidation was very limited during the whole period of cold exposure, since at all times tested there was either nil ammonia efflux or net absorption of ammonia and glutamine; i.e. the muscle was in positive nitrogen balance throughout the period studied. Thus most of the amino acid nitrogen taken up from the blood and not found in the free amino pools must have been incorporated into protein, since it was not oxidized, as shown by the glutamine and ammonia blance. The data on amino acid incorporation into proteins indicate that hind leg protein turnover is rapidly and widely modulated from a low initial setting upon cold exposure to a higher protein synthesis rate immediately afterwards, suggesting that protein turnover may have an important role in short-term events in cold-exposed muscle, in addition to its influence in long-term adaptation.