V. Capraro

Sugar and electrolyte absorption in the rat intestine perfused “in vivo”

Summary1.Studies are reported of rat intestinal perfusion “in vivo” in which data relating to the transport of sugars, sodium, fluid as well as intracellular concentrations of sugars and electrolytes have been obtained.2.A direct linear relationship with a zero intercept between net sodium and net sugar transport has been observed.3.The average intracellular concentration of sugars is always lower than in the luminal fluid and blood; this fact is consistent with the existence of a sugar pump located at the serosal pole of the absorbing cell.4.Intracellular sodium concentration is lower and intracellular potassium concentration is higher than in “in vitro” experíments.5.Cell sodium concentration and content as well as cell water content are increased by raising the luminal glucose concentration. In the same situation cell potassium concentration decreases while cell potassium content remains unchanged.6.Transport phenomena are more efficient in “in vivo” than in “in vitro” experiments.

Extracellular space determination in rat small intestine by using markers of different molecular weights.

The apparent extracellular space (ECS) of rat jejunum, everted and cannulated “in vitro”, has been measured by using extracellular markers of different molecular weights. The markers used were two polyethyleneglycols,14C and3H labelled (14C-PEG MW 4000 and3H-PEG MW 900) and3H-sucrose. The ECSs for the mucosal and serosal sides have been separately determined throughout the time course, and it has been found that the two spaces are identical when PEG 4000 was used but the serosal ECS is almost the double when using PEG 900. The serosal ECS determined with sucrose is four times as big as the mucosal ECS. It seems reasonable to conclude that the best marker for the measure of total apparent ECS is sucrose, placed in the serosal compartment, taking into account that the mucosal ECS is four times smaller than the serosal one. All the markers used reach equilibrium with ECS, more rapidly in the mucosal than in the serosal ECS.Finally, by comparing cell water and cell Na concentrations, one observes that there is a statistical difference between the results obtained by using PEG 4000 as an extracellular marker and those obtained with sucrose.

Energy-rich phosphates and transintestinal transport in rat intestine incubated in vitro at different temperatures.

In the present work, the transported fluid and the tissue content of ATP, ADP and AMP has been evaluated in the jejunum rat intestine which was everted and incubated in vitro both at 28 degrees C and at 38 degrees C for 1 h. The energy-rich phosphates have been measured in the tissue at the beginning and at the end of the experiment as well as in vivo. These determinations have been made in the total intestine and in the scraped mucosa. ATP and ADP content are higher in vivo and lower but constant at 28 degrees C in vitro; on the contrary, at 38 degrees C in vitro, the initial and final content of these adenilic nucleotides are both lower than at 28 degrees C. Under all these conditions the AMP content does not vary appreciably. Wet weight to dry weight ratios ahve been reported for mucosal and submucosal tissues in unincubated and incubated intestines. In some experiments, fluid transport (measured as an actual serosal volume increase) was determined every 20 min during a 1-h incubation. At 28 degrees C, fluid transport is constant throughout the time of the experiment, but at 38 degrees C, there is a progressive decrease of the transported fluid. Fluid transport and ATP content of the intestine seem to be directly related. The transport activity which is lower at 38 degrees C than at 28 degrees C, seems to be due to a low availability of energy-rich phosphates.

Effect of sodium on passive permeability of non-electrolytes through the intestinal wall

Der Einfluss des Natriums auf die passive Permeabilität der Jejunum-Schleimhaut der Laboratoriumsratte gegenüber wasserlöslichen, nichtmetabolisierbaren und elektroneutralen Substanzen (Thioharnstoff, Azetamid) wurde untersucht. Wird das Natrium des NaCl in der Perfusionsflüssigkeit durch Trisoder Cholin-Kationen ersetzt, so nehmen sowohl der transepitheliale Glukosetransport wie auch die Mobilität der geprüften Substanzen ab.

Effect on ethyl acetate on the transport of sodium and glucose in the hamster small intestine in vitro

The effect of ethyl acetate on Na+, water and glucose transport, as well as on glucose and electrolyte intracellular concentrations in everted and cannulated sacs of hamster jejunum, have been studied. Ethyl acetate, a substance that easily penetrates and delivers energy to the cell, strongly stimulates net glucose and Na+ transport. The explanation of the experimental results takes into account the possibility of the existence of an active extrusion of glucose at the level of the basolateral membrane of the enterocyte.

The rat and hamster jejunum during transintestinal transport in vitro.

By using the jejunal tract of rat and hamster intestine, net fluid transintestinal transport in the everted sac incubated in vitro at 28 degrees C and at 38 degrees C has been determined. In the scraped mucosa wet weight/dry weight ratio, cell water, sodium and potassium concentration have been detected in vivo and in vitro, throughout the incubation time, at the two different temperatures. Under all these conditions ATP, ADP and AMP levels have been determined in total intestine and in scraped mucosa. In rat jejunum incubated in vitro at 38 degrees C transintestinal fluid transport continuously decreases during 1-h experiment; in the same time the enterocyte gains sodium, dilutes cell potassium and swells, whereas its energy charge is dramatically reduced. All these parameters are constant in rat jejunum incubated at 28 degrees C and in the hamster incubated both at 28 degrees C and at 38 degrees C throughout the experiment. An inadequate diffusion of oxygen into the enterocyte, could tentatively explain experimental results obtained on rat jejunum at 38 degrees C. Under all tested conditions, energy charge and intracellular potassium are lower in conditions in vitro than in those in vivo; the contrary happens for cell sodium and swelling. The oxygenation of the intestine in vitro, lower than the one in vivo, could explain the different behaviour found in the two experimental conditions.

The extracellular space of rat intestine "in vivo".

SummaryThe extracellular space (ECS) of rat jejunum, ileum and colon were determined in “in vivo” condition both by means of a continuous perfusion technique and after ligature of the renal pedicles. As a marker, intravenously injected14C-polyethylenglycol (14C-PEG) was used.The data indicate that the ECS of rats whose renal pedicles were ligated, increases throughout the experiment, due most probably to a hypertonic expansion of the extracellular space. On the contrary, in the experiments with a continuous perfusion the ECS remains constant throughout the experiment.Total tissue water does not change in the two types of experiments whereas the intracellular water decreases only if the renal pedicles are ligated.

Hyperglycemia and net transintestinal glucose and sodium transport in the rat.

Hyperglycemia produced by intravenous infusion of glucose causes, in the everted jejunum of rat, an increase of net transintestinal transport of glucose, Na and water without modifying their cell concentration. The concentration of glucose in the fluid pouring out at the serosal side is higher than the calculated intracellular concentration, especially in the experiments in which the serosal compartment is initially empty. This fact could be explained by the possible existence of an active extrusion mechanism in the basolateral membrane of the enterocyte.

Solvent drag on urea and thiourea across small intestine of Testudo hermanni and Bufo bufo urinary bladder.

Abstract 1. 1. Small intestine of Testudo hermanni and Bufo bufo urinary bladder placed in vitro between two isotonic perfusing fluids present a net flux of thiourea and urea from the mucosal to the serosal side. 2. 2. The net flux of these solutes occurs in the same direction as the volumetric flux. 3. 3. Treatment with ouabain 2 × 10 −4 M abolishes thiourea net flux across the small intestine and lowers the volumetric flux. 4. 4. Posthypophyseal hormones increase urea net flux across the bladder as well as the volumetric flux. 5. 5. Most probably the net flux of these substances is caused by solvent drag effect.

A Sodium Dependent, Non-Carrier Mediated Transport of a Passive Diffusing Substance across the Intestinal Wall

It is commonly accepted that sodium concentration in the bathing mucosal fluid strongly affects the transport of substances which are actively transported through the intestinal barrier (1, 2).