Relationship between antipyrine absorption and blood flow rate in rat jejunum,ileum, and colon

Summary The appearance rate of antipyrine in intestinal venous blood was measured in anesthetized rats during perfusion (0.2 ml/min) of a buffered solution with 1 mmol/l labeled antipyrine through a jejunal, ileal, or colonic segment (length: 2–5 cm). When the blood flow rate was increased from 0.9–1.2 to 1.6–2.0 ml min^–1 g^–1 by raising the systemic blood pressure from 80 to 130 mm Hg, the absorption of antipyrine increased only in the colon. Stepwise reduction of the blood flow rate from 1.4–1.7 to 0.2–0.3 or stepwise raise from 0.2–0.3 to 1.4 ml min^–1 g^–1 by constriction or release of the mesenteric artery decreased or increased the absorption rate of antipyrine. The relation between absorption and flow rate can be described by curves which ascend at low and level off into a horizontal section at high flow rates. At the same blood flow rate the regional absorption rate decreased in the order jejunum, ileum, and colon with the largest step between ileum and colon. Model analysis yielded the following results for jejunum, ileum, and colon, respectively: permeability-surface area product 0.083, 0.074, and 0.037 ml min^–1 g^–1; fraction of absorptive site blood flow rate 0.24, 0.19, 0.08. The differences can be attributed mainly to the change of the surface area from jejunum to ileum and colon. Send offprint requests to D. Winne at the above address     

Blood flow in intestinal absorption models

Up to the present, ten models have been proposed or applied to analyze the relationship between blood flow and intestinal absorption. The conceptions of these models and their basic and final equations are described. In addition, their relationship to the first-order rate constants used in the models not explicitly including the blood flow rate is elucidated. Usually a curvilinear (concave curvature) relationship between the blood flow rate and the absorption rate is predicted by the models. This similarity of the curves is the reason that in many cases several models are compatible with the experimental data.     

The effect of inhibitors of folic acid absorption on the transfer rate constants in the rat everted proximal jejunum: A method for their evaluation from a three-compartment model

When solute transfer through the intestinal in vitro everted sac preparation is described by a three-compartment system, solute transfer rate constants can be derived for the mucosal and serosal permeability barriers. A catenary variant has been presented as well as a mammillary one where paracellular movement of solute is additionally allowed for. The first order differential rate equations governing the change in solute concentration in all three compartments with respect to time have been solved and the explicit analytical solutions provided. Since these solutions are cumbersome to use in the estimation of the required rate constants, a least squares procedure has been applied directly to the differential form of the rate equations in order to derive the rate constants without recourse to the analytical solutions. Verification of the solutions and of the estimated rate constants was by substitution of the latter into the former to test the goodness of fit for folic acid absorption data. Both variants take into account the simultaneous fluid movement which occurs during absorption experiments and which complicates the interpretation of absorption data. The mammillary model showed that only 10% of folic acid movement could pass directly through the paracellular pathways and that the bulk of folate movement is probably through the epithelial cells. However the catenary model without paracellular movement gave just as good fit to the data and was used subsequently. Experiments investigating the effect of substances implicated in folate malabsorption were analyzed in terms of the catenary model for folic acid absorption, in order to investigate their effects on the transfer rate constants free from the complicating effects on fluid movement. When pronounced inhibition took place, as with methotrexate, the mucosal rate constants were reduced, whereas the serosal rate constants were elevated. Also, the forward (k₁₂) mucosal rate constant correlated significantly with the overall folate transfer in contrast to the other rate constants. These observations are consonant with the concept of a mucosally sited entry step exerting a controlling influence over the transfer rate of folic acid rather than a serosally sited exit process and with the conclusion that this may be the site of action of substances causing folate malabsorption.     

Effects of in situ and systemic lindane treatment on in vivo absorption of galactose and leucine in rat jejunum

 In vivo intestinal absorption of L-leucine is significantly decreased by the presence of lindane (0.3, 0.2 and 0.1 mM) in perfusion solution (in situ lindane treatment) for 5 min. The inhibitory effect is earlier when lindane concentration is higher, and it is irreversible. There are no changes in D-galactose absorption when lindane (0.3 and 0.2 mM) is perfused for 5 min, but a significant decrease is observed if pesticide is perfused for 10 min at 0.3 mM concentration. Subcutaneous lindane treatment at a dose of 68.76 μmol/kg over 7 days does not alter D-galactose and L-leucine absorption. In situ lindane treatment (0.3, 0.2 and 0.1 mM) induces a significant decrease in basolateral (Na⁺-K⁺)-ATPase activity. In contrast, systemic lindane treatment (s.c. injection) at doses of 34.38 and 68.76 μmol/kg over 7 days does not alter this enzyme activity, although a significant decrease is observed in rats injected s.c. with 68.76 μmol/kg lindane over 15 days. Received: 21 November 1995/accepted: 21 February 1996     

Dependence of intestinal absorption in vivo on the unstirred layer

Summary The appearance rate of butanol, antipyrine, salicylic acid, and urea in the venous blood of rat jejunal loops perfused in vivo is increased up to 64%, if the intraluminal solution is mixed more efficiently by the simultaneous perfusion of air. The enhancement of the absorption can be attributed partly to the enlarged absorbing area but mainly to the reduction of the effective unstirred layer thickness by about 500 m. The unstirred layer reduces the phenylalanine absorption at 0.1 mmol l^–1 but not at 100 mmol l^–1, since at high concentrations a full saturation of the transport system can be achieved in spite of the unstirred layer resistance. The interference of the unstirred layer increases with increasing absorbability of the substances.     

大鼠在体单向肠灌流法对核黄素肠吸收的研究

目的：研究核黄素在大鼠肠道的在体吸收情况。方法应用大鼠在体肠灌流技术中的重量法研究核黄素在大鼠的十二指肠、空肠、回肠的吸收情况,用高效液相色谱法测定肠灌流液中核黄素的含量,计算核黄素的有效渗透系数（Pef）及药物吸收速率常数（Ka ）。结果核黄素在大鼠各肠段的 Pef（×10－4 cm·s －1）按十二指肠、空肠、回肠顺序依次分别为1.002±0.630、0.818±0.386、0.796±0.372;Ka （×10－3 s －1）依次为1.114±0.625、0.905±0.452、0.873±0.369。结论核黄素在大鼠肠段不同部位吸收存在差异,核黄素在十二指肠的吸收显著高于空肠和回肠段。     

Influence of dietary fiber and intraluminal pressure on absorption and pre-epithelial diffusion resistance (unstirred layer) in rat jejunum in situ

Summary The appearance rates of antipyrine, benzoic acid, benzylamine, urea, and-methyl-D-glucoside (MG) in jejunal venous blood of anesthetized rats were measured with and without dietary fibers methylcellulose, carboxymethylcellulose sodium, guaran, and sodium alginate in the luminal solution. Raising the concentration of methylcellulose from 0 to 17.5 g/l resulted in an exponential increase in the viscosity of the solution to 98 cSt, a linear decrease of the diffusion coefficient for antipyrine by 28%, and an increase in antipyrine absorption in the perfused jejunal segment by 23%. The simultaneous increase in intraluminal pressure and radius resulted in a linear relation between absorption rate and apparent mucosal surface area. Similar results were obtained by raising intraluminal pressure directly using a carbohydrate-free perfusion solution. In the perfused rat jejunum, the effect of increased pre-epithelial diffusion resistance (i.e. reduced diffusion coefficient and lengthened diffusion distance) induced by methylcellulose on absorption was overcome by the effect of the enlarged apparent mucosal surface area. Preperfusion of a substrate-free, guaran containing solution followed by perfusion with a guaran-free solution containing antipyrine and MG retarded the increase in the appearance rate of these substrates due to the additional viscous guaran layer left after preperfusion.Constant distension of the intestinal wall was achieved by injecting 0.5 ml of the solution into a closed jejunal segment. Addition of the carbohydrates to the injection solution (approx. 100 cSt viscosity) resulted in a 3% to 20% reduction in the diffusion coefficients and in the absorption of antipyrine, benzoic acid, and MG. Diffusion coefficients for urea and benzylamine were reduced by 5% to 12%; absorption varied in the range of the control (–22% to +43%). Model analysis revealed that, in the closed jejunal segment of the rat, the limiting step in the closed process of antipyrine, benzoic acid, and MG was pre-epithelial diffusion resistance; the reduction of absorption, therefore, corresponded roughly to that of the diffusion coefficient. In the case of urea and benzylamine, pre-epithelial diffusion resistance was only 20% of the total permeation resistance: the influence of the polymers on absorption, therefore, was not always significant.     

In vitro permeation of beta-lactam antibiotics across rat jejunum and its correlation with oral bioavailability in humans

AIMS: To investigate the correlation between in vitro permeation of 11 beta-lactam antibiotics across rat jejunum and their oral bioavailability in humans. METHODS: The absorptive and secretory permeation across rat jejunum was evaluated and apparent permeability coefficients (P(app)) were determined. RESULTS: A steep, sigmoid-type curve was obtained for the relationship between P(app) in the absorptive permeation and human oral bioavailability. When the ratios of P(app) in the absorptive direction to P(app) in the secretory direction were plotted against human oral bioavailability, a much improved correlation was obtained (r = 0.98, P < 0.001). The addition of glycylglycine to both mucosal and serosal media modified the permeation of ceftibuten and cephalexin from the absorptive to the secretory direction. CONCLUSIONS: For 11 beta-lactam antibiotics rat intestinal permeation correlated well with human oral bioavailability, especially when corrected for secretory transport.     

Factors influencing the transfer of xanthines across the everted rat jejunum

A number of factors having the potential to influence the transfer of theophylline across the everted rat jejunum were examined. The transfer of several other xanthine derivatives was also investigated. Strophanthin-K and 2,4-dinitrophenol had no effect on theophylline transfer. The transfer of theophylline from a 2:1 complex with phenobarbital was identical to that of theophylline alone. Magnesium ion (120 mM) and hypertonicity (600 mOsm) had no effect on the transfer of theophylline at pH 5.5. With the exception of xanthine, the clearance of all of the xanthine homologs tested was related to their partition coefficients in a chloroform/pH 7.4 phosphate buffer.     

增液汤的体内肠吸收评价研究

目的：探讨增液汤的肠吸收特性。方法通过HPLC对增液汤的肠吸收特性进行初步研究。结果增液汤中5－羟糠醛、肉桂酸、甲基麦冬黄烷酮A和甲基麦冬黄烷酮B在整个肠段吸收较好。哈帕俄苷、安格洛苷C介于难吸收与易吸收之间,十二指肠的吸收明显高于回肠和空肠段。结论增液汤的肠吸收研究,可能为其效应物质基础研究提供科学指导。     

Absorption,Distribution and Metabolism of Sulphafurazole and Chloramphenicol in Rats with Intestinal Occlusion

Abstract The rat small intestine was occluded at the ileocaecal junction, while control rats underwent sham–operation. 42–46 hours later sulphafurazole 50 mg/kg or chloramphenicol 250 mg/kg was given by gavage. The drug concentrations in the whole blood, small intestine, large intestine, liver, kidneys, lungs and heart at respectively 30 and 60 min. after sulphafurazole and at 60 min. after chloramphenicol administration were assayed chemically. Occlusion increased the absolute liver and small intestinal weights. The total sulphafurazole levels reached in blood and other tissues except the large intestine at 30 min. were about similar at 60 min. both in sham–operated and occlusion rats, but occlusion increased total sulphafurazole in the large intestine at 60 min. Occlusion increased acetyl sulphafurazole in the liver, kidneys and lungs at 60 min. and in the large intestine acetyl sulphafurazole was higher at 60 min. (about 60 %) than at 30 min. (about 30 %) in both sham–operated and occlusion rats. Occlusion did not significantly modify total chloramphenicol in any tissue or blood. Occlusion increased free and NO₂–reduced chloramphenicol in the large intestine. It seems that occlusion does not alter the absorption or distribution of sulphafurazole and chloramphenicol, but modifies their inactivation by increasing metabolism and probably by altering their excretion through the large intestine.     

Absorption of paraquat by rat gut in vitro

The absorption of radioactively labeled paraquat was measured in rat ileum, jejunum and colon by a micro everted sac technique (Semenza and Mühlhaupt, 1969). The absorption rate increased linearly over the range of concentrations measured (10^–5 to 10^–2 M) and was enhanced by nearly 50% in the absence of sodium ions. The absorption rate decreased in the order: ileum, jejunum, colon whereby in the colon still 65% of the values of the small intestine were observed.     

天山雪莲提取物主要成分的大鼠在体肠吸收动力学

目的:研究天山雪莲主要活性成分绿原酸和芦丁的大鼠在体肠吸收动力学。方法:采用单向灌流实验技术,利用HPLC法测定绿原酸和芦丁的量,分别研究药物质量浓度及吸收部位对绿原酸和芦丁吸收的影响。结果:药物质量浓度对绿原酸和芦丁吸收速率常数(Ka)和表观吸收系数(Papp)无显著性影响;绿原酸和芦丁在小肠各段间吸收的Ka和Papp无显著性差异,但与结肠相比吸收明显增大。结论:一定范围的药物浓度对绿原酸和芦丁的Ka和Papp无显著性影响,其吸收机制为被动扩散。药物在全肠道吸收较好,吸收窗主要在小肠,且小肠内无明显的特定吸收部位。     

Coir fibre toxicity: In vivo and in vitro studies

The biological activity of coir fibre, coir ash and their components were investigated in vitro by measuring the haemolytic activity and macrophage cytotoxicity. In vivo studies carried out by injecting guinea pigs intratracheally with coir fibres resulted in resolving granulomas. The observed haemolytic activity and macrophage cytotoxicity was more marked with coir ash compared with coir fibres. Chemical analysis of coir ash revealed the presence of toxic chemical constituents in appreciable amounts.     

Rat jejunum perfused in situ: Effect of perfusion rate and intraluminal radius on absorption rate and effective unstirred layer thickness

Summary In anaesthetized rats a jejunal segment was perfused in situ varying the perfusion rate (0.1, 0.2, 0.5 ml/min) in a randomized order. The intraluminal radius of the segments was small (1.7 mm) or enlarged (3.1 mm) by increasing the intraluminal pressure. The appearance rate of butanol, antipyrine, salicylic acid, d-and l-phenylalanine but not of urea in the venous blood of the jejunal segments was increased up to 35 %, when the intraluminal perfusion rate was raised from 0.1 to 0.5 ml/min. Two factors contribute to this effect: the flattening of the concentration gradient down the segment and the reduction of the effective unstirred layer thickness. The length and the intraluminal radius of the perfused segments was not altered, when the perfusion rate was varied. Therefore, a change of the absorbing area did not contribute to the increase of the absorption rate induced by the increase of the perfusion rate. In the series with small intraluminal radius the experimental data corresponded to the theoretical predictions obtained for a laminar intraluminal flow. In the segments with enlarged intraluminal radius the increase of the absorption rate by raising the perfusion rate was less than expected for a laminar flow indicating that the flow might have been turbulent. The enlargement of the intraluminal radius from 1.7 to 3.1 mm increased the absorption rate up to 100%.     

Assessment and modulation of acamprosate intestinal absorption: comparative studies using in situ, in vitro (CACO-2 cell monolayers) and in vivo models

The purpose of this study was to explore the intestinal absorption mechanism of acamprosate and to attempt to improve the bioavailability (BA) of the drug through modulation of its intestinal absorption using two enhancers (polysorbate 80 and sodium caprate) based on in situ, in vitro and in vivo models and comparing the results obtained. Intestinal transport of the drug, in the absence and in presence of polysorbate 80 (0.06, 0.28 and 9.6 mM) or sodium caprate (13 and 16 mM) was measured by using an in situ rat gut technique and Caco-2 cell monolayers. Additionally, the effect of sodium caprate on drug oral bioavailability, measured as urinary recovery, was quantified by performing in vivo experiments with the rat as animal model. Only sodium caprate was able to increase the absorption rate constant (ka) of acamprosate in the mid-intestine of the rats from 0.29 +/- 0.07 h-1 in the absence of the promoter to 0.51 +/- 0.19 h-1 in the presence of C10 16 mM, along with the apparent permeability (Papp) obtained in Caco-2 cells (around two-fold). However, the drug bioavailability in rats (around 20%) did not improve in the presence of any of the concentrations tested (13, 16 and 50 mM). It is concluded that acamprosate absorption likely occurs via paracellular pathway and can be enhanced by sodium caprate in situ and in vitro but not in vivo-thus suggesting that although in situ and in vitro studies could be useful in early screening to select a potential promoter, in vivo studies in animal models are necessary to confirm the utility of the enhancer and to determine the influence of physiological variables.     

Influence of intestinal efflux pumps on the absorption and transport of furosemide

Purpose

Furosemide is a commonly used diuretic which is used in the treatment of edema, congestive heart failure, hypertension and renal failure. Its absorption exhibits inter- and intra-subject variability that can be attributed to many factors including the intestinal efflux pumps such as the P-glycoprotein (P-gp). This study was done due to the great disagreement between what is published in the literature regarding the influence of P-gp on furosemide and at the same time due to the importance of this drug in the treatment of different conditions as described above. In addition, an investigation of the effect of two of the commonly used pharmaceutical excipients (hydroxypropyl β-cyclodextrin [HPβCD] and Tween 80) and also a P-gp inhibitor (verapamil hydrochloride) on the intestinal absorption of this drug were also done.

Methods

The study utilized the everted intestinal sacs technique to investigate both the effect of the efflux transporter (P-gp) on furosemide absorption and also the effect of the chosen excipients.

Results

The absorption of furosemide was significantly influenced by the P-gp as confirmed by the everted vis the non-everted sacs together with the verapamil study in which the transport of furosemide was inhibited by verapamil. In addition, Tween 80 was also shown to inhibit the P-gp pump whereas the HPβCD did not significantly influence the efflux of furosemide in this study.

Conclusions

P-glycoprotein and some of the used excipients in the formulation play a very important role in the transport of furosemide and other drugs. Thus excipients that affect the activity of P-gp should be avoided when formulating drugs that are substrate for the P-gp or other efflux pumps.     

艾片的大鼠在体肠吸收动力学研究

目的:研究艾片的大鼠在体肠吸收动力学。方法:采用大鼠在体单向灌流实验,利用气相色谱法测定艾片中龙脑含量,分别研究灌流流速、药物浓度、吸收部位对艾片吸收的影响。结果:灌流流速、药物浓度、吸收部位对艾片吸收速度常数(Ka)和表观吸收系数(Papp)无显著性影响。结论:艾片的肠吸收机制为被动扩散,其吸收动力学符合一级方程。     

穗花杉双黄酮大鼠在体肠吸收动力学的研究

采用大鼠在体单向肠灌流实验模型,用HPLC-UV法测定灌流液中药物浓度,研究穗花杉双黄酮肠吸收动力学。结果表明穗花杉双黄酮在十二指肠、空肠、回肠和结肠的吸收速率常数（Ka）、药物表观渗透系数（Papp）差异无统计学意义（P>0.05）,提高药物浓度的吸收速率常数基本保持不变。在大鼠各肠段均有吸收,无特定吸收部位,吸收机制为被动扩散。