Reduced sodium absorption in the colon under serotonin is a potential factor aggravating secretory diarrhea

BACKGROUND

Serotonin is a substance with a propulsive effect on the gastrointestinal tract. It stimulates the intestinal secretion of water and electrolytes, and plays an important role in the pathophysiology of secretory diarrhea. However, the influence of serotonin on intestinal absorption is very poorly understood.

OBJECTIVES

This study aimed to evaluate the serotonin and selected antagonists of serotonin receptors, i.e., ondansetron (5-HT3) and GR113808 (5-HT4), on electrogenic sodium ion absorption in the colon.

MATERIAL AND METHODS

The electrophysiologic method developed by Ussing and modified with a stimulating function on the mucosal side of the isolated colon wall was used. The influence of selected serotonergic compounds on the electrogenic transport of sodium ions under stationary conditions and mechanical stimulation was investigated. For this purpose, experiments were performed on specimens of isolated rabbit colon. Amiloride and bumetanide were used as reagents directly controlling individual ion transport. The data were analyzed using tests for paired samples (paired sample t-test, Wilcoxon signed-rank test and one-sided sign test).

RESULTS

Serotonin reduced stationary and stimulated colonic sodium absorption. The 5-HT3 receptor antagonist did not influence the studied phenomenon, while 5-HT4 antagonists acted contrary to serotonin.

CONCLUSIONS

Serotonin reduces both stationary and stimulated sodium ion absorption, thus playing an important role in the pathophysiology of secretory diarrhea. The described phenomenon depends on serotonin's action on 5-HT4 receptors.

The bi-phased course of electrophysiological response of isolated snail intestine on mechanical stimulation

The transepithelial potential difference and changes of diameter of isolated snail intestine as index of its motility were studied in immersed bath in control conditions and after gentle stimulation by 60 seconds of washing of the intestinal lumen. Immediate depolarization and 20% augmentation of the lumen were observed during the stimulation. After stimulation, additional transient depolarization of the transepithelial potential difference and gradual diminution of intestine lumen back to control values over a period of 20 minutes occurred. The immediate reaction was greatly influenced by the presence of sodium or chloride ion transport inhibitors, however, the late phase of the response was not. It is hypothesized that changes of transepithelial electrogenic ion transport and of intestinal motility during the stimulation mirror the inflow of intestinal content and after completion of stimulation may be related to its storage.

The electrical potential difference through the foot epithelium of the snail Achatina achatina, Lameere during mechanical and chemical stimulation

An important electrophysiological variable--the transepithelial potential difference reflects the electrogenic transepithelial ion currents, which are produced and modified by ion transport processes in polarized cells of epithelium. These processes result from coordinated function of transporters in apical and basolateral cell membranes and have been observed in all epithelial tissues studied so far. The experiments were performed on isolated specimens of snail foot. In the experiments, the baseline transepithelial electrical potential difference--PD, changes of transepithelial difference during mechanical stimulation--dPD and the transepithelial resistance were measured with an Ussing apparatus. A total of 60 samples of foot ventral surface of 28 snails were studied. The transepithelial electrical potential difference of isolated foot ranged from -6.0 to 10.0 mV under different experimental conditions. Mechanical stimulation of foot ventral surface caused changes of electrogenic ion transport, observed as transient hyperpolarization (electrical potential difference became more positive). When the transepithelial electrical potential difference decreased during stimulation, the reaction was described as depolarization. When amiloride and bumetanide were added to the stimulating fluid so that the sodium and chloride ion transport pathways were inhibited, prolonged depolarization occurred. Under the influence of different stimuli: mechanical (gentle rinsing), chemical (changes of ion concentrations) and pharmacological (application of ion inhibitors), transient changes of potential difference (dPD) were evoked, ranging from about -0.7 to almost 2.0 mV. Changes in transepithelial potential difference of the pedal surface of the snail's foot related to these physiological stimuli are probably involved in the locomotion of the animal and are under control of the part of the nervous system in which tachykinin related peptides (TRP) act as transmitters.

Mebeverine influences sodium ion transport in the distal colon

The study was performed to check if the well-known intestinal spasmolytic effect of mebeverine is paralleled by any changes in intestinal transepithelial currents. The transepithelial potential difference related to ionic currents of the isolated rabbit distal colon wall was measured by means of Ussing's technique under control conditions and after gentle mechanical stimulation of intestinal epithelial surface by a flux from peristaltic pump and with and without of mebeverine in stimulation fluid. The transient hyperpolarization after mechanical stimulation was diminished after addition of mebeverine to the stimulation fluid when chloride transport was inhibited by bumetanide (BUME) but in the presence of amiloride (AMI), a sodium ion transport inhibitor, the drug did not influence the reaction. It was inferred that mebeverine was able to modulate transepithelial sodium ion transport and in this way to modify interaction between colonic wall and its contents during intestinal passage.

Comparison of the influence of halothane and isoflurane on airway transepithelial potential difference

Bidirectional transport of Na+ and Cl- ions by the epithelium controls production and composition of airway surface liquid and airway transepithelial potential difference and in these ways supports mucociliary transport. Volatile anesthetics are able to inhibit epithelial ion transport processes when applied at high concentration and have been suggested to elicit depression of airway clearance and both these effects could be involved in postoperative pulmonary complications. The goal of these studies was to reveal possible influence of halothane and isoflurane at lower concentrations on electrogenic ion transport in airway epithelium. These studies were performed on the isolated rabbit tracheal wall mounted in the Ussing chamber. The reaction of the preparation to the gentle mechanical stimulation performed as a jet flux was examined without or in the presence of anesthetics at concentration equivalent to 0.5 minimal anesthetic concentration of volatile anesthetics in pulmonary alveoli (MAC), 1 MAC, 2 MAC, 5 MAC and 10 MAC. The volatile anesthetics at concentrations equivalent to 5 and 10 MAC affected airway transepithelial potential difference and influenced hyperpolarization or depolarization reactions which occurred after mechanical stimulation. The above effects were present when Na+ transport was inhibited by amiloride. The disturbed epithelial Cl- transport may be proposed as an explanation of the action of volatile anesthetics on electrophysiological parameters of the isolated tracheal wall although the influence of anesthetics on tachykinin secretion from C-fiber endings, which are present in the preparation, should also be taken into consideration. The long-lasting action (tens of minutes) of volatile anesthetics on the isolated tracheal wall should be also studied in the future as a model of airway reaction to prolonged volatile anesthesia.

[Evaluation of low density lipoprotein oxidation in a course of hypothyroidism]

INTRODUCTION

The aim of this study was to evaluate the influence of hypothyroidism on oxidative modification of low density lipoprotein (LDL).

MATERIAL AND METHODS

24 patients with overt hypothyroidism and 10 patients with mild hypothyroidism were enrolled to the study. The control group consisted of 24 healthy subjects with normal serum TSH. Plasma level of oxidized LDL (oxLDL) and serum level of antibodies against oxidized LDL (anti-oxLDL) determined lipoprotein oxidation.

RESULTS

Significantly increased plasma oxLDL levels were found in patients with overt hypothyroidism in comparison to patients with mild hypothyroidism and control group. Anti-oxLDL levels in patients with overt or mild hypothyroidism and in the control group showed no significant differences. OxLDL plasma levels in patients with hypothyroidism inversely correlated with FT(4) levels and positively correlated with TSH, total cholesterol, LDL cholesterol and triglycerides levels.

CONCLUSIONS

The presented study indicates increased lipoprotein oxidation in patients with hypothyroidism which depends on the degree of hypothyroidism and changes in lipid profile. Elevated cholesterol and triglycerides levels are the factors increasing lipoprotein oxidation. Plasma oxLDL levels may constitute a useful marker indicating the risk for atherosclerosis in hypothyroidism.

The influence of ambroxol and capsaicin on the isolated rabbit bladder wall

Unmyelinated C-fibers endings lye beneath the epithelial layer and release neuropeptides which regulate baseline transepithelial potential difference (PD) and changes of transepithelial potential difference during mechanical stimulation (dPD). Ambroxol can suppress reflexes such as the cough or the corneal reflex which are connected to stimulation of C fibre endings. The study aimed to estimate the influence of ambroxol (ABX) and capsaicin (CAPSA) on PD and dPD in isolated rabbit bladder. The experiments were carried out on 26 bladder specimens of. 2 cm2 surface area each, obtained from 13 rabbits. Ussing apparatus was used. Procedure used for stimulation of sensory receptor involved directing stream onto epithelium. A stimulus lasted 30s, ejecting the 2.5 ml fluid. Amiloride and bumetanide were used to estimate of ionic currents. Each significant reaction was repeated at least 10 times on various specimens. PD ranged between 5 and 10 mV in different experimental conditions. Mechanical stimulation of isolated bladder wall caused increasing dPD about 2 mV defined as hyperpolarization. Application of ABX to the stimulation fluid decreased the hyperpolarization in comparison with control stimulation under conditions of inhibited chloride ion transport. Application of CAPSA to the stimulation fluid decreased the hyperpolarization in comparison with control stimulation under conditions of inhibited sodium ion transport. ABX and CAPSA had no influence on PD after mechanical stimulation. ABX as well as CAPSA influence on transepithelial ion transport pathways in bladder epithelium is dependent on sensory stimulation. ABX can be suspected to suppress bladder contractions.

Effects of halothane and isoflurane on stimulated airway transepithelial ion transport

Volatile anesthetics are suggested to elicit depression of airway clearance. The involvement of changes in transepithelial ion transport in this inhibition has already been observed. The Ussing method was used to study the changes in mechanical stimulation evoked electrogenic ion transport in isolated rabbit tracheal wall in the presence of halothane and isoflurane. The drugs dissolved in Ringer solution were directed as a flux from peristaltic pump to mucosal surface of trachea. In experimental settings without or with amiloride, the anestethics elicited reversible inhibition of stimulated ion transport and depolarization of transepithelial potential difference. Participation of chloride ion transport in observed changes is suggested. In the light of this study with application of anesthetics at higher concentrations than clinically relevant, the possibility of disturbances of airway transepithelial ion transport by clinically relevant concentration should be checked.

Postmortem examination of transepithelial ion currents in rabbit colon and trachea in relation to temperature of storage and its importance for interlethal reactions

Electrical phenomena resulting from transepithelial ion transport have been a subject of clinical, physiological, pharmacologic and toxicologic studies. These examinations concern mainly electric phenomena in live organisms. The changes of transepithelial ion pathways which take place postmortem have not been yet established. The aim of the study was an attempt to trace variability of electrophysiological parameters related to transepithelial ion transport in specimens of rabbit trachea and colon depending on temperature at which specimens were stored after death. It was observed that postmortem electric phenomena in epithelium of airways and alimentary tract of rabbit occur well-ordered but with slower course in trachea samples and in tissues which were preserved at low temperature after death.