Kinetics of uptake of glucose in rabbit jejunum: influence of sodium, unstirred layers, and passive permeation

1983 ◽  
Vol 61 (10) ◽  
pp. 1129-1137 ◽  
Author(s):  
A. B. R. Thomson
Keyword(s):  
Glucose Uptake ◽  
Intestinal Transport ◽  
Water Layer ◽  
Lauryl Alcohol ◽  
Unstirred Layer ◽  
Transport Rate ◽  
Rabbit Jejunum ◽  
Layer Resistance ◽  
Kinetics Of Uptake

Failure to account for the effect of the unstirred water layer and the contribution of passive permeation will lead to errors in the estimation of the kinetic constants of glucose uptake into the intestine. It is widely accepted that variations in the concentration of sodium in the bulk phase profoundly influence the rate of uptake of glucose in the intestine, but the kinetic basis for this effect remains in dispute. Accordingly, a previously validated in vitro technique was used to assess the effect of Na+ on the uptake of glucose into rabbit jejunum under conditions selected to reduce the unstirred layer resistance. Varying Na+ had no effect on the uptake of lauryl alcohol and therefore on unstirred layer resistance. The passive permeability coefficient for glucose uptake was estimated from the uptake of L-glucose, of D-glucose at 4 °C, or in the presence of 1 mM phlorizin or 40 mM galactose. The permeability for glucose increased as Na+ rose. The values of both the maximal transport rate and the Michaelis constant (Km) were influenced by Na+. A linear relationship was noted between Na+ and the maximal transport rate; the value of Km fell as Na+ was increased to 75 mequiv./L, but Km did not decline further with higher values of Na+. These results support the theoretical predictions of the presence of both an affinity and a velocity effect of the sodium gradient on the intestinal transport system for glucose.

Uptake of cholesterol into rabbit jejunum using three in vitro techniques: importance of bile acid micelles and unstirred layer resistance

1981 ◽  
Vol 241 (3) ◽  
pp. G270-G274
Author(s):  
A. B. Thomson ◽  
B. D. O'Brien
Keyword(s):  
Bile Acid ◽  
Water Layer ◽  
Effective Resistance ◽  
Bulk Phase ◽  
Unstirred Layer ◽  
Cholesterol Concentration ◽  
Unstirred Water Layer ◽  
In Vitro Techniques ◽  
Rabbit Jejunum

The rate of uptake (Jd) of cholesterol into the intestine is influenced by the effective resistance of the unstirred water layer, the concentration of the probe molecule at the aqueous-membrane interface, and the passive permeability characteristics of the membrane. This study was undertaken to determine the influence of the bile acid micelle and the unstirred water layer on the Jd of cholesterol into rabbit jejunum, using everted sacs, full-thickness biopsies, and disks. When the bulk phase was stirred and the resistance of the unstirred layer was low, there was a linear relation between cholesterol concentration in the bulk phase and Jd when the concentration of taurodeoxycholic acid (TDC) was constant, but increasing TDC in the presence of a constant concentration of cholesterol was associated with a decline in Jd. When the concentration of both TDC and cholesterol was varied but the ratio of TDC to cholesterol was maintained constant, Jd increased slightly. The Jd of cholesterol was higher into sacs than into biopsies, which in turn was greater than into disks; Jd into disks was much lower when the resistance of the unstirred layer was high. These results suggest that 1) the bile acid micelle serves to provide a reservoir for partitioning of the cholesterol from the micelle into the aqueous phase from which the cholesterol is absorbed; 2) the Jd of cholesterol into disks of jejunum is influenced by the effective resistance of the unstirred water layer; and 3) although the quantity of cholesterol Jd varies markedly between sacs, biopsies, and disks, the qualitative aspects of the role of the bile acid micelle in cholesterol absorption were similar using the different in vitro techniques.

The Influence of Carbohydrate Gelling Agents on Rat Intestinal Transport of Monosaccharides and Neutral Amino Acids in Vitro

1980 ◽  
Vol 59 (5) ◽  
pp. 373-380 ◽  
Author(s):  
B. Elsenhans ◽  
U. Süfke ◽  
R. Blume ◽  
W. F. Caspary
Keyword(s):  
Intestinal Absorption ◽  
Membrane Filtration ◽  
Intestinal Transport ◽  
Michaelis Constant ◽  
Experimental Conditions ◽  
Plant Polysaccharides ◽  
Gelling Agents ◽  
Layer Resistance ◽  
Filtration Technique

1. In the present investigation with rings of everted rat small intestine, carbohydrate gelling agents (plant polysaccharides) such as guaran, pectin, tragacanth, carubin and carrageenan were employed to study their direct effect on intestinal absorption of α-methyl-d-glucoside, d-galactose, l-leucine and l-phenylalanine. 2. Inhibition was found to correlate with the viscosity of the incubation medium, a function only of the polysaccharide concentration, and was independent of other properties of the carbohydrate gelling agents. 3. Reversal of this inhibition was achieved either by washing the tissue free of polysaccharide or by raising tissue agitation. 4. Uptake kinetics in polysaccharide-containing solutions revealed a marked increase of the apparent Michaelis constant although the maximal transport capacity remained essentially unaltered. 5. Since there was no binding of the substrate by the polysaccharides under experimental conditions as judged by a membrane filtration technique, it is concluded that carbohydrate gelling agents may impair intestinal absorption by means of an increased unstirred layer resistance.

Effect of chronic ingestion of ethanol on in vitro uptake of lipids and glucose in the rabbit jejunum

1984 ◽  
Vol 246 (2) ◽  
pp. G120-G129
Author(s):  
A. B. Thomson
Keyword(s):  
Fatty Acids ◽  
Food Intake ◽  
Weight Control ◽  
Bulk Phase ◽  
Unstirred Layer ◽  
Control Group ◽  
Cholesterol Uptake ◽  
Incremental Change ◽  
Rabbit Jejunum

This study was undertaken to determine the effect of chronic feeding of ethanol on the in vitro jejunal uptake of lipids and glucose. The first group of rabbits was fed ad libitum (CAL); the food intake of a second control group [weight control (WC)] was restricted to match their gain in body weight with that of a chronically ethanol-fed group (ETH); and the food intake of a third control group [food control (FC)] was restricted to match the food intake with that of ETH. There was a marked decline in cholesterol uptake in WC and FC compared with CAL, and cholesterol uptake in ETH was intermediate between the higher value in CAL and the lower value in WC and FC. The uptake of fatty acids 4:0-12:0 was similar in the CAL, FC, WC, and ETH groups, both when the bulk phase was stirred and unstirred; the uptake of fatty acids 16:0 and 18:0 was lower in WC and FC than in CAL; and the uptake of fatty acids 14:0, 16:0, and 18:0 was even lower in ETH. The uptake of a homologous series of fatty alcohols was greater in WC and ETH than in CAL at five different rates of stirring of the bulk phase. When the uptake of fatty acids 6:0-12:0 was corrected for unstirred layer resistance, a linear relation was noted between fatty acid chain length and the natural logarithm of rate of uptake/aqueous diffusion coefficient, and the steeper slope in WC and ETH than in CAL represented a higher incremental change in free energy. Glucose uptake was similar in CAL, WC, and FC but was greater in ETH from 5 to 40 mM glucose. These studies demonstrate that 1) weight restriction, food restriction, and chronic ethanol feeding are associated with a change in the effective resistance of the unstirred layer and in the passive permeability properties of the rabbit jejunum, and 2) ethanol has a differential effect on passive permeation of short-, medium-, and long-chain fatty acids and cholesterol.

Diffusion barriers to passive lipid uptake of canine posterior tracheal epithelium

1982 ◽  
Vol 52 (5) ◽  
pp. 1223-1229
Author(s):  
S. F. Man ◽  
A. B. Thomson
Keyword(s):  
Surface Area ◽  
Lipid Membrane ◽  
Water Layer ◽  
Diffusion Barriers ◽  
Unstirred Layer ◽  
Tracheal Epithelium ◽  
Lipid Uptake ◽  
Incremental Change ◽  
Tracheal Epithelial

In studies of passive uptake of canine posterior tracheal epithelium in vitro, we examined the effective resistance of the unstirred water layer (UWL) when the bulk phase of the preparation was stirred and unstirred. Rates of uptake of fatty acids were corrected for unstirred layer effects. The incremental change in free energy, derived from the linear relationship between uptake and chain length of lipids, was -271 cal/mol. Measurement of the effective thickness (d) and surface area (SW) of the UWL showed that d fell and SW rose as the rate of stirring increased. SW was less than 15% of the tracheal epithelial cell membrane's surface area. It is concluded that 1) lipid membrane of the tracheal epithelium and the overlying UWL represent the major diffusion barriers for lipid uptake across the tracheal epithelium; 2) failure to correct for the UWL resistance leads to serious errors in the estimates of permeability properties of the epithelium to lipids; and 3) the unstirred layer severely limits the proportion of cell membrane available for transport in vitro.

Intestinal kinetic parameters: effects of unstirred layers and transport preparation

1980 ◽  
Vol 239 (5) ◽  
pp. G372-G377 ◽  
Author(s):  
A. B. Thomson ◽  
J. M. Dietschy
Keyword(s):  
Kinetic Parameters ◽  
Water Layer ◽  
Bulk Phase ◽  
Passive Component ◽  
Tissue Preparation ◽  
Apparent Permeability ◽  
Rabbit Jejunum ◽  
Everted Sacs

Three in vitro tissue preparations were used to derive kinetic parameters for the transport of D-glucose in rabbit jejunum, and the resistance of the unstirred water layer was varied by altering the rate of stirring of the bulk phase. The apparent permeability coefficient (Pd*) of the rabbit jejunum for D-glucose was much higher from everted sacs and full-thickness biopsies than from intestinal discs. Failure to adjust the experimentally determined flux for the contribution of the passive component led to errors in the estimation of the maximal transport rate (Jdm) and in the apparent Michaelis constant (Km*). Jdm was higher in biopsies than everted sacs or discs, Km was also higher in biopsies. With each tissue preparation Km* and Pd* were markedly influenced by stirring the bulk phase, whereas Jdm was unchanged. The results indicate that failure to account for the effect of the passive component and the unstirred layer leads to major errors in the estimation of Km*, Pd*, and Jdm. Furthermore, the magnitude of these kinetic constants is influenced by the type of in vitro system used to derive the constants, and it is therefore invalid to extrapolate the results obtained using one preparation to those utilizing another preparation, or to the in vivo situation.

Uptake of l-Leucyl-l-Leucine and Glycylsarcosine by Hamster Jejunum in Vitro

1983 ◽  
Vol 65 (2) ◽  
pp. 177-184 ◽  
Author(s):  
D. M. Matthews ◽  
D. Burston
Keyword(s):  
Amino Acid ◽  
Intestinal Transport ◽  
Inhibitory Effect ◽  
Complete Inhibition ◽  
Maximal Velocity ◽  
Uptake System ◽  
Apparent Affinity ◽  
Kinetics Of Uptake ◽  
Dipeptide Uptake

1. Preliminary observations of the effects on intestinal transport of the lipophilic properties of the amino acid side chains of a series of neutral dipeptides showed that, contrary to expectation, l-valyl-l-valine and not l-leucyl-l-leucine was the most powerful inhibitor of uptake of the hydrolysis-resistant dipeptide glycylsarcosine by hamster jejunum in vitro. 2. Investigation of the kinetic characteristics of uptake of l-leucyl-l-leucine showed that Kt and Vmax. were lower than the corresponding values for l-valyl-l-valine, suggesting a higher apparent affinity for transport and a lower maximal velocity of transport. Ki for the inhibitory effect of l-leucyl-l-leucine on uptake of glycylsarcosine was less than one-half of the Kt for l-leucyl-l-leucine, so that inhibition was stronger than that expected from the apparent affinity for transport obtained from the kinetics of uptake of the inhibitor. In spite of this, l-leucyl-l-leucine was a much less powerful inhibitor of uptake of glycylsarcosine than was l-valyl-l-valine. 3. The results suggest that total uptake of l-leucyl-l-leucine at pH 5 is the result of at least two processes: uptake of intact peptide by one or more mechanisms, and also hydrolysis followed by uptake of free amino acid. At most concentrations, more than half the mediated uptake of l-leucyl-l-leucine was in the form of intact peptide. 4. The results of experiments on competition for uptake between dipeptides were unexpected. l-leucyl-l-leucine could inhibit mediated uptake of intact glycylsarcosine completely, but glycylsarcosine could not cause complete inhibition of mediated uptake of intact l-leucyl-l-leucine. Glycylsarcosine could, however, cause complete inhibition of mediated uptake of intact l-valyl-l-valine, which in turn could cause complete inhibition of mediated uptake of intact l-leucyl-l-leucine. The existence of more than one dipeptide uptake system in the small intestine seems probable.

Experimental diabetes and intestinal barriers to absorption

1983 ◽  
Vol 244 (2) ◽  
pp. G151-G159 ◽  
Author(s):  
A. B. Thomson
Keyword(s):  
Fatty Acids ◽  
Saturated Fatty Acids ◽  
Water Layer ◽  
Lauryl Alcohol ◽  
Fatty Acid Uptake ◽  
Effective Resistance ◽  
Acid Uptake ◽  
Passive Permeability ◽  
In Vitro Techniques

The unstirred water layer (UWL) and the brush-border membrane represent the major barriers to intestinal absorption. Enhanced uptake of several nutrients has been described in diabetes mellitus, and this study was undertaken in the rat to define whether these absorptive changes are due to alterations in the characteristics of these barriers. Using in vitro techniques the effective resistance of UWL was measured with lauryl alcohol, the rate of uptake (Jd) of which is limited by diffusion across the UWL. At all rates of stirring of the bulk phase, the effective resistance of UWL was less in diabetic than control rats. The Jd of a homologous series of saturated fatty acids (4:0-18:0) and cholesterol was higher than disks of intestine of diabetic than control intestine; this enhanced uptake of lipid could not be demonstrated using intestinal biopsies. The change in incremental free energy of transfer of fatty acid uptake into disks was higher in diabetic than control animals after correction for UWL effects. After correction for UWL, the Michaelis constant for Jd of D-glucose was similar in diabetic and control jejunum, and the greater Jd of glucose in diabetics was due to a higher maximal transport rate (Jmd) and a higher passive permeability coefficient. It is concluded that the enhanced uptake of glucose, fatty acids, fatty alcohols, and cholesterol into diabetic intestine is due to a reduction in the effective resistance of the UWL, an increase in the passive permeability properties of the membrane, and a rise in the Jmd for D-glucose.

Mechanisms of intestinal adaptation: unstirred layer resistance and membrane transport

1984 ◽  
Vol 62 (6) ◽  
pp. 678-682 ◽  
Author(s):  
A. B. R. Thomson
Keyword(s):  
Kinetic Parameters ◽  
Molecular Mechanisms ◽  
Intestinal Adaptation ◽  
Intestinal Transport ◽  
Lauryl Alcohol ◽  
Transport Processes ◽  
Unstirred Layer ◽  
Incremental Change ◽  
Medium Chain Length ◽  
Acute And Chronic Exposure

The effect of the resistance of unstirred water layers (UWL) on the kinetic parameters of active and passive intestinal transport processes is well established, but the possibility of adaptive changes in the resistance of this diffusion barrier in health and disease has only recently been appreciated. The rate of uptake (Jd) of a homologous series of saturated fatty alcohols into the jejunum is limited by diffusion through the UWL. The Jd of lauryl alcohol has been determined at different rates of stirring of the bulk phase and at different sites along the intestine, in animals of different ages, in varying species, in rats with streptozotocin-induced diabetes mellitus, following abdominal irradiation, after acute and chronic exposure to ethanol and after the feeding of various diets. The UWL varies in response to most of these experimental manipulations. After correcting for unstirred layer effects, the incremental change in free energy (∫ΔFW → l) of the uptake of medium chain-length fatty acids and the maximal transport rate ([Formula: see text]) and Michaelis constant (Km) for glucose uptake were determined. These kinetic parameters changed in many of these experimental manipulations. However, there was no correlation between changes in UWL, ∫ΔFw → l, [Formula: see text], Km or [Formula: see text]/Km. It is concluded that (1) the intestine is capable of adapting to a variety of physiological and pathological challenges; and (2) the major kinetic changes included UWL, ∫ΔFW → l[Formula: see text] and Km. The molecular mechanisms responsible for these changes in the dimensions and characteristics of the barriers to intestinal transport must now be defined.

Jejunal uptake of sugars, cholesterol, fatty acids, and fatty alcohols in vivo in diabetic rats

1985 ◽  
Vol 63 (11) ◽  
pp. 1356-1361
Author(s):  
C. Hotke ◽  
Y. McIntyre ◽  
A. B. R. Thomson
Keyword(s):  
Fatty Acids ◽  
Lauric Acid ◽  
Water Layer ◽  
Diabetic Rats ◽  
The Body ◽  
Unstirred Layer ◽  
Unstirred Water Layer ◽  
Uptake Of Nutrients

Previous in vitro studies have demonstrated enhanced active and passive intestinal uptake of nutrients in streptozotocin-diabetic rats, but the effect of diabetes on the in vivo absorption of glucose and amino acids remains controversial, and the effect of diabetes on the in vivo uptake of lipids has not been reported. Accordingly, an in vivo perfusion technique was used in rats to examine the uptake of nutrients from the intestinal lumen, their transfer to the body, their mucosal and submucosal content, and the percentage of uptake transferred. Diabetes was associated with reduced uptake of fatty alcohols, indicating that the effective resistance of the unstirred water layer in vivo is higher in diabetic than in nondiabetic control rats. The mucosal and submucosal content of dodecanol was lower in diabetic than in control rats, but the percentage of the dodecanol uptake transferred to the body was higher. Although the uptake of varying concentrations of D-galactose was similar in diabetic and in control animals, kinetic analysis corrected for unstirred layer effects demonstrated lower mean values of the passive permeability coefficients (Pd) for galactose in diabetic than in control animals, with lower values of the Michaelis constant (Km) and higher values of the maximal transport rate [Formula: see text]. The uptake of lauric acid was reduced in diabetic rats, whereas the uptake of deconoic acid and of cholesterol was unchanged. With correction for unstirred layer effects, it was apparent that the jejunum of diabetic rats was in fact more permeable to decanoic and lauric acid as well as to cholesterol. The results suggest that (i) in diabetic rats the effective resistance of the unstirred water layer between the jejunal lumen and the brush border membrane is lower; (ii) the differences in unstirred layer resistance between the diabetic and control animals obscure the changes in the kinetic constants (Pd, Km, [Formula: see text]) describing the uptake of galactose, medium chain length fatty acids and cholesterol; and (iii) the kinetic changes in nutrient uptake observed in vitro may be confirmed in vivo once the effect of intestinal unstirred layers has been taken into account.

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