在体单向肠灌流模型研究白芷中三种成分的吸收特性

目的:研究白芷中有效成分欧前胡素、异欧前胡素和花椒毒酚在大鼠小肠各段的吸收特征。方法:采用大鼠在体单向肠灌流模型结合HPLC法同时测定肠灌流液中欧前胡素、异欧前胡素和花椒毒酚含量的变化,考察高、中、低三组剂量下三种成分在十二指肠、空肠和回肠的吸收特性。结果:三种成分随着剂量的增大,吸收速率常数(Ka)和有效渗透系数(Peff)逐渐增大。三种成分相同剂量下各肠段间吸收均无显著性差异,其吸收大小顺序为:欧前胡素异欧前胡素花椒毒酚。结论:白芷三种主要成分在各肠段均吸收良好,吸收大小呈剂量相关性。     

小肠锌吸收动力学模型中锌吸收速率常数K_(21)/K_(12)比值与锌吸收率的关系探讨

用二房室动力学模型研究了原位灌流的大鼠空肠锌吸收速率常数K_(21)/K_(12)比值与锌吸收率的关系,结果表明K_(21)/K_(12)比值与锌吸收率的相关系数不受动物状态及各种处理的影响,可用于探讨锌吸收机理.     

创伤后血二胺氧化酶的变化与肠粘膜损伤

探讨创伤感染对肠道屏障功能的影响。以山羊、大鼠手术+失血再灌注+内毒素(LPS),大鼠肠缺血再灌注和犬低温枪伤多种创伤动物为模型,测定血浆二胺氧化酶(DAO)活性,并测定血乳酶、TNF和LPS含量。观察小肠病理形态改变。结果:失血再灌注后血浆DAO水平显著升高,给予内毒素后山羊血DAO水平再度升高。血浆DAO的变化与血乳酸,TNF和LPS变化呈高度相关(r=0.872,0.842和0.817,p<0.01)。光、电镜检查表明肠粘膜损伤,失血再灌注损伤可致肠粘膜屏障功能损伤,测定血浆DAO活性变化对判断小肠粘膜损伤有帮助     

失血性休克复苏后肠内给予特殊营养物对肠粘膜血流量的影响

为探讨失血性休克复苏后肠内营养与肠粘膜血流改变的关系 ,从SD大鼠开腹制作空肠袋 ,将激光多谱勒探头和肠粘膜张力计放置在空肠袋两端 ,根据动物分组分别向袋内注射葡萄糖、谷氨酰胺、丙氨酸及甘露醇。复制失血性休克模型 (30mmHg ,维持 6 0min) ,然后用林格氏液复苏 ,恢复灌流 6 0min。分别测定肠粘膜血流量和局部PCO2 张力 (PrCO2 )。结果显示 ,失血性休克和复苏过程中 ,谷氨酰胺和葡萄糖组粘膜血流量比甘露醇和丙氨酸组显著增加 ,PrCO2 显著降低 ;而肠内给予丙氨酸进一步降低肠粘膜血流量 ,升高PrCO2 。提示 :失血性休克复苏后 ,肠内给予丙氨酸减少肠粘膜血流量 ;而给予谷氨酰胺和葡萄糖能增加肠粘膜血流量 ,对缺血再灌流损伤的肠道提供保护作用     

肠缺血再灌注时肠内给予不同营养物对肠粘膜ATP含量的影响

将SD大鼠分组 ,先制作空肠袋 ,分别向袋内注射不同营养物 :10mmol/L丙氨酸 ,10mmol/L葡萄糖 ,10mmol/L甘露醇或 5mmol/L丙氨酸 +5mmol/L葡萄糖的混合液 ,用动脉夹阻断肠系膜上动脉血流 6 0min后 ,再恢复灌流 6 0min。分别于阻断血流 6 0min和恢复灌注 6 0min测定肠粘膜ATP含量。研究结果显示 ,缺血再灌注能显著降低肠粘膜ATP含量 ,给予丙氨酸或葡萄糖 /丙氨酸混合液使肠粘膜ATP含量进一步降低 (P <0 .0 1) ,而给予葡萄糖能显著增加肠粘膜ATP含量 (P <0 .0 1)。结论 :缺血再灌注过程中 ,肠内给予葡萄糖能改善肠粘膜ATP含量 ,对缺血再灌注损伤的肠道提供保护作用     

普伐他汀大鼠在体肠吸收动力学

目的:研究普伐他汀在大鼠小肠的吸收情况。方法:采用大鼠在体小肠回流实验装置,利用HPLC紫外检测的方法测定肠循环液中酚红和普伐他汀的含量。采用XTerra@MS C-18色谱柱(5μm,150mm×2.1 mm.ID),流动相为3.5 mmol/L磷酸二氢钠溶液—乙腈(70:30,用磷酸调至pH 3.0),流速为0.2ml/min;结果:普伐他汀在大鼠小肠全肠段的吸收速率常数和吸收百分率分别为0.110±0.023(h~(-1))和18.21±2.50%。普伐他汀在小肠中吸收量与时间呈线性关系,但吸收速率较低。结论:普伐他汀可以通过增加药物的脂溶性,进而提高药物的生物利用度。     

小肠吸收机能的离体研究方法

自Auchinachie等人较详细地研究了离体小肠的通透性机能以后,近十年来又有不少工作从事于离体情况下小肠吸收机能的研究。其原则方法多不外在离体情况下,用两个彼此隔离的灌流系统分别灌流浆膜及粘膜侧空间,经过一定时间后,由两侧物质浓度的改变,得知小肠粘膜的主动转移活动。Wilson等又用外翻的离体小肠(即粘膜被翻转朝外)进行实验。依此原理,Crane及Wilson提出之方法实有许多优点(如     

胰岛素对大鼠空肠和回肠锌吸收动力学作用的研究

用原位灌流的大鼠空肠和回肠研究了胰岛素对锌吸收动力学的作用。糖尿病大鼠血清胰岛素水平明显减低,空肠锌吸收速率常数K_(12)和K_(21)分别比对照组增大50％和31％,K_(20)减小59％;胰岛素治疗组血清胰岛素水平稍有恢复,空肠K值变化不大。糖尿病组回肠K_(12)和K_(21)分别比对照组减小29％和8％,K_(20)变化很小;胰岛素治疗组K_(12)和K_(21)分别比对照组增大36％和51％,K_(20)变化不大。糖尿病组空肠锌吸收慢速相半衰期比对照组增大29倍,胰岛素治疗组明显小于糖尿病组。糖尿病组K_(12)和K_(21)的空肠/回肠比值比对照组增大110％和41％,K_(20)的空肠/回肠比值减小57％;胰岛素治疗组K_(12)和K_(21)的空肠/回肠比值恢复到对照水平,K(20)的比值有所恢复。上述结果提示,胰岛素对锌从粘膜到血液的转运过程有促进作用,并对小肠锌吸收部位有一定影响。     

柠檬酸发酵的数学模型研究

对柠檬酸发酵过程中菌体生长、基质消耗及产物生成的动力学进行了研究,得到了描述柠檬酸发酵过程的数学模型,并蹦实验统计数据为基础,通过对模型进行分析,推断了模型参数,同时用实验结果对模型进行了验证,结果表明模型计算与实测结果拟合良好,从而显示所建立的模型基本正确地描述了柠檬酸发酵过程,这对应用电子计算机控制发酵过程,实现发酵过程的最佳化有着重要意义。     

体循环肠灌流法研究红禾麻提取物在类风湿性关节炎大鼠与正常大鼠体内的肠吸收差异

比较红禾麻提取物在AA大鼠与正常大鼠体内的肠吸收差异。实验采用体循环肠灌流法,建立大鼠RA模型,应用UPLC-MS/MS检测肠灌流液中新绿原酸、绿原酸、隐绿原酸、芦丁、异槲皮苷、槲皮苷、山奈酚-3-O-芸香糖苷、木犀草苷的含量,探究各成分在不同因素(pH值、药物浓度、肠段、胆汁和P-gp抑制剂)下的肠吸收特性。结果表明,槲皮苷的吸收方式为主动转运,其余7个成分的吸收方式为被动扩散。除绿原酸、隐绿原酸外,正常状态下各成分以回肠吸收最好,病理状态下以十二指肠吸收最好,推测药物吸收的特定部位会受疾病状态的影响而发生改变。各成分的吸收均受pH、胆汁和P-gp的影响,其中,槲皮苷可能是P-gp的底物。RA能影响红禾麻提取物在大鼠体内的肠吸收,其作用机制尚需进一步研究。     

Understanding glucose transport by the bacterial phosphoenolpyruvate:glycose phosphotransferase system on the basis of kinetic measurements in vitro

The kinetic parameters in vitro of the components of the phosphoenolpyruvate:glycose phosphotransferase system (PTS) in enteric bacteria were collected. To address the issue of whether the behavior in vivo of the PTS can be understood in terms of these enzyme kinetics, a detailed kinetic model was constructed. Each overall phosphotransfer reaction was separated into two elementary reactions, the first entailing association of the phosphoryl donor and acceptor into a complex and the second entailing dissociation of the complex into dephosphorylated donor and phosphorylated acceptor. Literature data on the K(m) values and association constants of PTS proteins for their substrates, as well as equilibrium and rate constants for the overall phosphotransfer reactions, were related to the rate constants of the elementary steps in a set of equations; the rate constants could be calculated by solving these equations simultaneously. No kinetic parameters were fitted. As calculated by the model, the kinetic parameter values in vitro could describe experimental results in vivo when varying each of the PTS protein concentrations individually while keeping the other protein concentrations constant. Using the same kinetic constants, but adjusting the protein concentrations in the model to those present in cell-free extracts, the model could reproduce experiments in vitro analyzing the dependence of the flux on the total PTS protein concentration. For modeling conditions in vivo it was crucial that the PTS protein concentrations be implemented at their high in vivo values. The model suggests a new interpretation of results hitherto not understood; in vivo, the major fraction of the PTS proteins may exist as complexes with other PTS proteins or boundary metabolites, whereas in vitro, the fraction of complexed proteins is much smaller.     

Kinetics of the absorption of amino acids by the rat intestine in vivo

The kinetics of l-phenylalanine and l-lysine absorption by the rat small intestine in vivo have been studied by perfusing intestinal segments and monitoring simultaneously the uptake of the substrate into the intestinal tissue and its disappearance from the perfusate.The rate of phenylalanine disappearance is a linear function of the substrate concentration. Its uptake into the tissue is rapid and obeys saturation kinetics, but is not concentrative. Both tissue uptake and disappearance rate can be inhibited by leucine or methionine, but are not influenced by hydrophilic neutral or dibasic amino acids.Lysine disappearance from the perfusate and its uptake into the tissue both display saturation kinetics. Lysine transport is quantitatively smaller than that of phenylalanine. Both uptake and disappearance are inhibited by arginine and leucine, but are unaffected by other neutral amino acids or sugars.To analyse the kinetic results, integrated equations were developed to express the final concentration in the perfusate in terms of the original concentration. The disappearance rate was considered as a mixed process (saturable and non-saturable in parallel) in a one-compartment system, and the uptake by the tissue was treated as a two-compartment system in which the amino acid entered the cells by a mixed process but left them by a pure non-saturable mechanism.The results concerning disappearance from the lumen are compatible with the one-compartment model. Phenylalanine absorption can be described by a major non-saturable component and a minor saturable one, while lysine absorption occurs almost entirely by a saturable process. The two-compartment model does not adequately describe the tissue uptake results.     

Chymotrypsin-catalyzed peptide synthesis. Kinetic analysis of the kinetically controlled peptide-bond formation

The kinetics of peptide-bond formation catalyzed by delta-chymotrypsin has been studied for a number of peptide products of different length using fixed concentrations of the acyl component (Ac-Phe-OMe, Ac-Ala-Ala-Phe-OMe, or Ac-Ala-Ala-Tyr-OMe) and varying concentration of the amino component (H-Ala-NH2 or H-Ala-Ala-NH2). The time course of the reactions was followed by monitoring ester consumption and peptide product formation by analytical HPLC. On the basis of a plausible four-centre mechanistic model, the theoretical time course of these reactions was calculated using rate and equilibrium constants determined by separate kinetic experiments. The excellent agreement observed between the theoretical and the experimental time courses supports the proposed mechanism and provides evidence for the validity of the present kinetic approach. By focusing attention on the rate constants which are critical for efficient synthesis, this mechanistic information constitutes a valuable basis for the use of the enzymatic peptide synthesis in preparative applications.     

Influence of various fluorescent and non-fluorescent labels on the kinetics of the complex formation of alpha-chymotrypsin with basic pancreatic trypsin inhibitor (Kunitz).

The association of alpha-chymotrypsin with basic pancreatic trypsin inhibitor was studied using extrinsic signals produced by fluorescent and nonfluorescent labels. The reactive dyes were covalently bound to the proteins in the complexed state, in which the binding region was protected. The signals were sufficiently large to measure the complex formation at protein concentrations of 10(-9)M by fluorescence and down to 10(-6)M by absorption. Therefore, the association and dissociation could be followed over a broad range of concentration. Good correspondence was observed between data which were obtained with different labels and with published values for the unlabeled proteins. Existing differences could be explained by different buffer conditions used by the different authors. Also the pH dependence of the dissociation rate constants was essentially unaltered by the introduction of the labels. The large signals allowed a direct measurement of the equilibrium constants of dissociation, even at high pH, at which they are in the range of 10(-8)M. The experimentally determined binding constants were in agreement with those calculated from the rate constants. The temperature dependence of the binding constants revealed a small positive and pH-dependent enthalpy change [deltaHo = 4.0 kcal/mol (16.7 kJ) at H 7.0[. The results prove that the labeling can be performed in such a way that the equilibrium and kinetic parameters of the system studied are not significantly influenced.     

Kinetics of phenylalanine absorption by the rat intestine in vivo after distal resection

The kinetics of L-phenylalanine absorption across rat small intestine in sham and 50% distal resected animals, in vivo, have been studied by perfusing jejunal loops and monitoring the disappearance of the substrate from the perfusate. After 5 months postresection the total phenylalanine absorption was increased. The relationship between total absorption of substrate and its concentration in the bulk phase shows a non-saturable component and a saturable one that can be inhibited by methionine, both in control and remnant jejunum. The slope of the line that represents the non-saturable component is greater in remnant jejunum, indicating that the apparent mass-transfer coefficient, K'D, was increased by distal resection. The kinetic analysis of the saturable component shows that Jmax was unaltered and the apparent semisaturation constant, K'M, was slightly decreased by distal small intestine resection. Correction of the kinetic constant for the unstirred water layer effects shows that the differences between 'real' KD values of the two experimental groups increase whereas 'real' KM values do not change significantly. This indicates that the observed increase in total intestinal absorption in resected animals appears to result from an increase in the intestinal passive permeability.     

Re-interpretation of the logistic equation for batch microbial growth in relation to Monod kinetics

Aims:  To determine the underlying substrate utilization mechanism in the logistic equation for batch microbial growth by revealing the relationship between the logistic and Monod kinetics. Also, to determine the logistic rate constant in terms of Monod kinetic constants.
Methods and Results:  The logistic equation used to describe batch microbial growth was related to the Monod kinetics and found to be first-order in terms of the substrate and biomass concentrations. The logistic equation constant was also related to the Monod kinetic constants. Similarly, the substrate utilization kinetic equations were derived by using the logistic growth equation and related to the Monod kinetics.
Conclusion:  It is revaled that the logistic growth equation is a special form of the Monod growth kinetics when substrate limitation is first-order with respect to the substrate concentration. The logistic rate constant ( k ) is directly proportional to the maximum specific growth rate constant ( μ _m) and initial substrate concentration ( S ₀) and also inversely related to the saturation constant ( K _s).
Significance and Impact of the Study:  The semi-empirical logistic equation can be used instead of Monod kinetics at low substrate concentrations to describe batch microbial growth using the relationship between the logistic rate constant and the Monod kinetic constants.     

离体外翻肠囊法研究白及提取物中6种成分的肠吸收特性

为研究白及提取物中4-(葡萄糖氧基)-肉桂酸葡萄糖氧基苄酯(B12)、2-异丁基苹果酸(B6)、1-[4-(葡萄糖氧)苄基]-2-异丁基苹果酸酯(B17)、1,4-二[4-(葡萄糖氧)苄基]-2-异丁基苹果酸酯(B14)、二氢菲1(B19)和1,4-二[4-(葡萄糖氧)苄基]-2-异丁基苹果酸酯-2-[4-O-肉桂酰基-6-O-乙酰基]葡萄糖苷(B23)6个成分在大鼠小肠中的吸收动力学特性。实验采用大鼠离体外翻肠囊模型考察各成分在不同浓度、不同肠段的吸收特性,建立超高效液相色谱-三重四极杆串联质谱联用仪(UPLC-MS/MS)法测定各成分含量,计算累计吸收量和吸收速率常数。结果表明,除B6成分的低浓度外,各成分在不同浓度、不同肠段下均表现为线性吸收,其回归相关系数(R)均达到0.9以上,符合一级吸收速率,且吸收速率常数随着浓度的增加而增加,提示各成分吸收机制为被动吸收;在同一浓度下不同肠段的总体吸收趋势为十二指肠的吸收要大于回肠、结肠和空肠。综上,白及提取物中6种成分在小肠中均有吸收,但小肠对各成分的吸收具有选择性。本研究可为白及提取物的药物临床开发,确定药物剂型方面提供了一定的实验参考。     

Kinetic analysis of the entire RNA amplification process by Qbeta replicase

The kinetics of the RNA replication reaction by Qbeta replicase were investigated. Qbeta replicase is an RNA-dependent RNA polymerase responsible for replicating the RNA genome of coliphage Qbeta and plays a key role in the life cycle of the Qbeta phage. Although the RNA replication reaction using this enzyme has long been studied, a kinetic model that can describe the entire RNA amplification process has yet to be determined. In this study, we propose a kinetic model that is able to account for the entire RNA amplification process. The key to our proposed kinetic model is the consideration of nonproductive binding (i.e. binding of an enzyme to the RNA where the enzyme cannot initiate the reaction). By considering nonproductive binding and the notable enzyme inactivation we observed, the previous observations that remained unresolved could also be explained. Moreover, based on the kinetic model and the experimental results, we determined rate and equilibrium constants using template RNAs of various lengths. The proposed model and the obtained constants provide important information both for understanding the basis of Qbeta phage amplification and the applications using Qbeta replicase.     

Structural and functional analysis of glucose adsorption at high maltose concentrations in the rat small intestine in vivo

To elucidate the mechanism of glucose absorption at high substrate concentrations, we studied structural and ultrastructural peculiarities of enterocytes arranged at different levels along the intestinal villus. The preparations were obtained from an isolated segment of the rat small intestine after its perfusion with maltose solutions with both low (25 mM) and high (100 mM) concentrations, respectively. Under conditions of chronic experiment at high substrate concentration, an enlargement of intercellular clefts, indicating glucose absorption, occurred in deeper areas of the villus. Besides, also in chronic experiment, we studied kinetics of maltose hydrolysis and derived glucose absorption in the isolated segment of the rat small intestine after its perfusion with maltose at superhigh (up to 200 mM) initial concentrations. Based on these data, a conclusion is made that active transport is the main mechanism of absorption of glucose derived from maltose hydrolysis, operating both at low disaccharide concentrations, and in the range of its superhigh (up to 200 mM) concentrations.