反刍动物肽代谢的研究进展

肽作为蛋白质的主要消化产物,是反刍动物和瘤胃微生物的重要营养来源。反刍动物的组织及瘤胃微生物都能利用肽作为氮源以维持其生长,且肽显示了比氨基酸更强的刺激瘤胃微生物生长的作用。反刍动物存在对肽和氨基酸不同的并行吸收机制,以确保机体在各种生理状态下的营养代谢的平衡。本文从瘤胃肽的产生和降解机制、吸收和营养作用、代谢调控等方面阐述了反刍动物肽的研究进展。     

硫和钴对反刍家畜利用尿素的影响（上）

反刍动物消化生理上的最大特点,在于它能更好地利用粗饲料,并能利用非蛋白含氮物。特别是后者是单胃家畜所无法比拟的。反刍动物的这一特性为合理利用大量的粗饲料资源和价格低廉的非蛋白含氮物提供了宽广的前景。当然,目前对反刍动物营养生理的研究还远不及对单胃动物和禽类的那样深广,但是,通过对瘤胃微生物区系及其特性的研究表明,反刍动物能为人类更好地提供动物性蛋白质,且其绝对量比猪和禽类多得多。因此,对反刍动物营养生理的研究越来越具有重要的意义。     

反刍动物对纤维素的消化利用及调控

反刍动物之所以能消化利用粗饲料中的纤维素等多糖类物质,是因为它们具有瘤胃这一独特的消化发酵罐,其内存在着大量的厌氧微生物。本文介绍了瘤胃内分解纤维素的主要微生物群,阐述纤维素在瘤胃内的降解、消化机制,并综述反刍动物对粗纤维利用的调控。     

反刍动物瘤胃蛋白质测定方法的研究进展

随着对反刍动物蛋白质营养和饲料营养价值评定研究的深入,传统的粗蛋白(CP)、可消化粗蛋白质(DCP)和蛋白质的生物学价值(BV)已经不能反映出反刍动物氮代谢的生理特点,为克服传统方法的缺陷,一些地区和国家开发出新的蛋白质体系.这些体系除了康奈尔碳水化合物-蛋白质体系外,共同特点是以小肠蛋白质为基础,包括瘤胃非降解蛋白质...     

大豆粕在反刍动物饲养业中的科学利用

采用适当的物理和化学方法对大豆粕进行处理,可提高反刍家畜对其蛋白质的利用率。对于反刍动物,蛋白质的消化部位影响其利用率。大豆蛋白在瘤胃中有60～80％被微生物降解,降解率颇高。如果能增加过瘤胃蛋白,则可提高其利用率。特别是对于高产的反刍动物来讲,瘤胃降解后经微生物合成的蛋白质仅能满足需求的一部分,另一部分则靠过瘤胃蛋白来满足。 近些年的研究表明,通过下述处理可达     

反刍动物瘤胃真菌的作用

真菌在反刍动物瘤胃内纤维物质消化过程中发挥重要作用，并参与瘤胃内蛋白质的降解过程，瘤胃真菌可以深入生长至植物纤维化组织内部，降解和利用其中的可溶性和结构性碳水化合物（如纤维素，半纤维素，果胶等），真菌在植物纤维组织中的穿透生长也为细菌充分分解和利用纤维物质创造了条件。     

反刍动物的氮代谢—历史的回顾,当前的认识及今后的展望

反刍动物的氮代谢是很多研究报告的主题。对于瘤胃和肠道功能的研究还在继续进行。许多试验已经表明了瘤胃微生物作为蛋白质来源在数量上和质量上具有重要性。控制微生物蛋白的合成或微生物的生长以及日粮蛋白的降解的各种因素已被揭示出来。关 于向反刍动物提供蛋白质的细节(瘤胃合成、过瘤胃日粮蛋白质、小肠消化)方面的知识已经有了相当的积累。相比之下当前对于反刍动物对氨基酸数量上的需要了解得还很不够。已经提出了一些描述反刍动物氮代谢的模型,这些模型综合了当前有关方面的各种知识。今后随着逐步加以修正,将有助于日粮的配合工作,更加充分地利用瘤胃发酵,提高反刍动物的生产效率。对于反刍动物氯代谢的进一步研究,将会更好地控制瘤胃发酵及瘤胃后的消化过程。     

保护饲料蛋白免受瘤胃微生物降解的方法

反刍动物所需蛋白来自瘤胃微生物蛋白和饲料未降解蛋白。对于维持饲养和低生产水平的奶牛,微生物蛋白和饲料未降解蛋白,甚至仅微生物蛋白就可以满足其需要,但对于快速生长犊牛和高产奶牛(尤其是泌乳初期),微生物蛋白和饲料未降解蛋白通常就不能满足其需要。由于在能量一定、氮源充足情况下,微生物产量相对稳定,所以解决这个矛盾的关键是增加饲料未降解蛋白或过瘤胃蛋白的数量。增加过瘤胃蛋白的途径有:     

瘤胃微生物调控技术研究进展

反刍动物的瘤胃就像一个庞大密闭的发酵罐,在整个消化过程中起着重要的作用.瘤胃功能的健康与否直接决定反刍动物的健康,因此使用一定的手段对瘤胃中降解与合成过程进行调控是可能的,也是必要的.本文对瘤胃微生物调控技术进行了综述.     

影响泌乳牛蛋白质利用的因素

影响反刍动物蛋白质利用的因素有饲料蛋白质的量与质(天然蛋白与非蛋白氮间的配比)、蛋白质在瘤胃的降解率、能量与氮之比率、饲料颗粒大小及其在瘤胃内的存留时间、供菌体蛋白合成的瘤胃内食物量、饲料蛋白质的理化处理方法和程度等。蛋白质和含氮物对反刍动物的效用,以蛋白质价值来计算;主要测定指标,是计算在上述各因素影响下进入小肠的氨基酸总量。但有人建议,     

Ammonia metabolism in exercise and fatigue: a review

Although fatigue is a well-known phenomenon and the phrase "exercised until exhaustion" is commonly understood, there is no unequivocal agreement on the fundamental nature of the fatigue process. Ammonia was linked to the development of fatigue as early as 1922, when ammonia production was observed from stimulated nerve and the question whether there could be a relationship between ammonia production and the muscle activity was raised. The immediate source of ammonia from muscle appears to be a result of the deamination of AMP and is more apparent in fast-twitch than in slow-twitch fibers. More recently, increases in blood ammonia levels have been reported in rats after swimming and in humans after arm work, maximal cycle ergometry, and treadmill exercise. Elevated blood ammonia has also been linked to a surprising variety of functional and metabolic neurological disturbances other than exercise and fatigue, including the development of hepatic coma, convulsions from ammonia toxicity precipitated by high-pressure oxygen breathing, epileptic seizures, and decreased neuronal excitability. In addition, a number of genetic disorders (inborn errors in metabolism, or IEMs) are characterized by elevated blood ammonia concentrations. Symptoms of neural disability in all of the above conditions have been related to the concentration of ammonia in blood. Although these studies do not relate to exercise or fatigue directly, it is conceivable that our understanding of the effect of high concentrations of blood ammonia in these clinical conditions may provide valuable insight into the effect of ammonia during exercise. This paper reviews the effect of ammonia production during exercise and other conditions upon purposeful activity and the development of fatigued states.     

肝硬化患者幽门螺杆菌感染与血氨的关系

 目的探讨肝硬化患者幽门螺杆菌(Helicobacter pylori,Hp)感染与血氨的关系.方法选择68例Hp阳性的乙型肝炎后肝硬化患者为阳性组,34例Hp阴性的乙型肝炎后肝硬化患者为阴性组,40例Hp阴性的健康检查者为对照组.分别检测各组的空腹血氨.阳性组病例治疗1周,停药4周后复查Hp,根治Hp后复查血氨.将阳性组病例分为大、中和少量感染组,根据肝功能Child分级进行分组,比较各组血氨水平.结果阳性组血氨浓度显著高于阴性组(P＜0.01);阴性组血氨浓度亦显著高于对照组(P＜0.01);Hp根治后血氨浓度显著下降(P＜0.01);大量感染组血氨浓度显著高于少量感染组(P＜0.05);阳性组中不同肝功能分级组血氨浓度之间有显著差异(P＜0.05),而阴性组中不同肝功能分级组血氨浓度之间无显著差异(P＞0.05).结论Hp感染与肝硬化的血氨浓度升高密切相关,易并发肝性脑病,根治Hp可使血氨水平显著降低,有利于防治肝性脑病.     

Exertional myalgia syndrome associated with diminished serum ammonia elevation in ischemic exercise testing.

A 36-year-old man with chronic severe exertional myalgias had a normal serum lactate elevation and diminished serum ammonia elevation on an ischemic forearm exercise test (IFET). The IFET is commonly performed in the evaluation of patients with complaints of exertional myalgias, cramps, and rhabdomyolysis. The finding of a normal serum lactate elevation and a diminished serum ammonia elevation after ischemic exercise is usually considered indicative of myoadenylate deaminase deficiency. However, myoadenylate deaminase activity was normal in this man's muscle biopsy specimen. This case suggests that a diminished serum ammonia elevation in the IFET is not always indicative of myoadenylate deaminase deficiency, a disorder of ammonia production. A diminished serum ammonia elevation in the IFET could also reflect an impairment of net ammonia efflux from muscle into blood.     

Positron emission tomography of hepatic first-pass metabolism of ammonia in pig.

Hepatic first-pass metabolism plays a key role in metabolic regulation and drug metabolism. Metabolic processes can be quantified in vivo by positron emission tomography scanning (PET). We wished to develop a PET technique to measure hepatic first-pass metabolism of ammonia. Seven anaesthetised pigs were given positron-labelled ammonia, (13)NH(3), into the portal vein and into the vena cava as successive 2-min infusions followed by 22-min dynamic liver scanning. Vena cava infusion data were used to account for recirculation of tracer and metabolites following the portal vein infusion. The scan data were analysed by a model of sinusoidal zonation of ammonia metabolism with periportal urea formation and perivenous formation of glutamine. The hepatic extraction fraction of (13)NH(3) was 0.73+/-0.16 (mean+/-SD, n=7 pigs). Values of clearance of ammonia to urea and to glutamine were obtained, as were rate constants for washout of these two metabolites. Overall, the modelling showed half of the ammonia uptake to be converted to urea and half to glutamine. The washout rate constant for glutamine was about one-tenth of that for urea. We conclude that hepatic first-pass metabolism of ammonia was successfully assessed by PET.     

Positron emission tomography of hepatic first-pass metabolism of ammonia in pig

Hepatic first-pass metabolism plays a key role in metabolic regulation and drug metabolism. Metabolic processes can be quantified in vivo by positron emission tomography scanning (PET). We wished to develop a PET technique to measure hepatic first-pass metabolism of ammonia. Seven anaesthetised pigs were given positron-labelled ammonia, ¹³NH₃, into the portal vein and into the vena cava as successive 2-min infusions followed by 22-min dynamic liver scanning. Vena cava infusion data were used to account for recirculation of tracer and metabolites following the portal vein infusion. The scan data were analysed by a model of sinusoidal zonation of ammonia metabolism with periportal urea formation and perivenous formation of glutamine. The hepatic extraction fraction of ¹³NH₃ was 0.73ǂ.16 (mean-SD, n=7 pigs). Values of clearance of ammonia to urea and to glutamine were obtained, as were rate constants for washout of these two metabolites. Overall, the modelling showed half of the ammonia uptake to be converted to urea and half to glutamine. The washout rate constant for glutamine was about one-tenth of that for urea. We conclude that hepatic first-pass metabolism of ammonia was successfully assessed by PET.     

Respiratory ammonia output and blood ammonia concentration during incremental exercise

The aim of this study was to investigate whether the increase of ammonia concentration and lactate concentration in blood was accompanied by an increased expiration of ammonia during graded exercise. Eleven healthy subjects performed an incremental cycle ergometer test. Blood ammonia, blood lactate and the amount of expired ammonia were measured until 30 minutes post exercise. The expired air was guided through a flow chamber filled with a sulphuric acid solution to trap the expired ammonia. Blood ammonia, blood lactate increased more than proportionally and the amount of expired ammonia (in micromol/min) increased exponentially with the workload. Post-exercise the amount of expired ammonia decreased within a few minutes back to pre-exercise levels while the concentrations of lactate and ammonia in blood decreased much more slowly and were still elevated after 30 minutes of recovery. We conclude that the more than proportional increase of ammonia and lactate during graded exercise, is accompanied with an exponential increase of expired ammonia output. Faster and more accurate ammonia gas detection techniques are necessary to quantify more precisely the respiratory ammonia output during graded exercise.     

Development of a SNP set for human identification: A set with high powers of discrimination which yields high genetic information from naturally degraded DNA samples in the Thai population

This study describes the development of a SNP typing system for human identification in the Thai population, in particular for extremely degraded DNA samples. A highly informative SNP marker set for forensic identification was identified, and a multiplex PCR-based Invader assay was developed. Fifty-one highly informative autosomal SNP markers and three sex determination SNP markers were amplified in two multiplex PCR reactions and then detected using Invader assay reactions. The average PCR product size was 71 base pairs. The match probability of the 54-SNP marker set in 124 Thai individuals was 1.48 × 10⁻²¹, higher than that of STR typing, suggesting that this 54-SNP marker set is beneficial for forensic identification in the Thai population. The selected SNP marker set was also evaluated in 90 artificially degraded samples, and in 128 naturally degraded DNA samples from real forensic casework which had shown no profiles or incomplete profiles when examined using a commercial STR typing system. A total of 56 degraded samples (44%) achieved the matching probability (PM) equivalent to STR gold standard analysis (successful genotyping of 44 SNP markers) for human identification. These data indicated that our novel 54-SNP marker set provides a very useful and valuable approach for forensic identification in the Thai population, especially in the case of highly to extremely degraded DNA.In summary, we have developed a set of 54 Thai-specific SNPs for human identification which have higher discrimination power than STR genotyping. The PCRs for these 54 SNP markers were successfully combined into two multiplex reactions and detected with an Invader assay. This novel SNP genotyping system also yields high levels of genetic information from naturally degraded samples, even though there are much more difficult to recover than artificially degraded samples.     

Metabolic fate of [13N]ammonia in human and canine blood

Nitrogen-13- ([13N]) ammonia is a widely used tracer for PET myocardial blood flow studies. Quantification of blood flow using tracer kinetic principles requires accurate determination of [13N]ammonia activity in blood. Since [13N] ammonia is rapidly metabolized, the arterial input function may be contaminated by labeled metabolites. We, therefore, characterized the 13N-labeled metabolites in blood after intravenous (i.v.) injection of 20 mCi [13N]ammonia in nine healthy volunteers. Utilizing a series of ion exchange resins, 13N-labeled compounds were separated into four groups: ammonia, neutral amino acids, acidic amino acids, and urea. Analysis of the metabolic fate of [13N]ammonia indicates that over 90% of the blood activity within the first two minutes after injection is present as [13N]ammonia. However, there is considerable contamination of the blood activity at 3-5 min by [13N]glutamine (amide) and urea, which collectively represent 18%-50% of the blood activity. Thus, correction of the arterial input function for 13N-metabolites is required to accurately quantify the arterial input function of [13N]ammonia in myocardial blood flow studies.     

Ammonia as an indicator of exercise stress implications of recent findings to sports medicine

The role of ammonia in exercise-induced fatigue is reviewed. Implications for integrated activity of developing hyperammoneic states, caused by various precipitating conditions such as exercise, liver dysfunction, hypoxia, hyperoxia, and chemical poisoning are described. The central role of ammonia in diverse important metabolic pathways indicates its ubiquitous role in a spectrum of activity ranging from elite exhaustive performance of sportsmen and -women to life-threatening organ dysfunction. The action of ammonia and metabolites from associated pathways in producing seemingly dangerous short term conditions, but inducing possible long term protection against degenerative processes associated with ageing (free radical-induced cellular damage) indicate the paradoxical position of ammonia and its associated metabolic pathways for health and disease processes.     

Evaluation of ammonia metabolism in the skeletal muscles of patients with cirrhosis using N-13 ammonia PET

OBJECTIVE: Skeletal muscle is said to compensate for the decreased ammonia metabolism in patients with cirrhosis. Branched-chain amino acids (BCAA) are being used as a treatment for hyperammonemia, and are believed to decrease blood ammonia by consumption of BCAA in skeletal muscles. We examined ammonia metabolism of the skeletal muscles in patients with liver cirrhosis after administration of BCAA using 13N-ammonia positron emission tomography (PET). METHODS: The subjects were patients with compensated or decompensated liver cirrhosis. PET studies were performed before and 2 hours after injection of BCAA. Serial dynamic PET scans (2 min x 10 frames) were started simultaneously with 13N-ammonia injection. The standardized uptake value (SUV) of both thighs was calculated. RESULTS: In the patient with compensated liver cirrhosis, there was little difference in the rate of increase in SUV before to after administration of BCAA. However, in the patient with decompensated liver cirrhosis, the rate of increase in SUV after administration was higher than that before administration of BCAA. CONCLUSION: Ammonia metabolism in the muscle of patients with liver cirrhosis could be examined noninvasively under physiological conditions using 13N-ammonia PET. The muscles were found to metabolize ammonia partially, and the role of this contribution to metabolism of ammonia in patients with decompensated liver cirrhosis is particularly important.