ION TRANSPORT IN ISOLATED RABBIT ILEUM. II. THE INTERACTION BETWEEN ACTIVE SODIUM AND ACTIVE SUGAR TRANSPORT

Assessing safety and efficacy of a novel glucose-free amino acid oral rehydration solution for watery diarrhea management in children: a randomized, controlled, phase III trial

Background

Diarrhoeal disease poses a significant global health challenge, especially in children under three years old. Despite the effectiveness of oral rehydration therapy (ORT), its adoption remains low. Glucose-based ORS (GORS) is the standard, but novel formulations like glucose-free amino acid-based VS002A have emerged as potential alternatives. This study aimed to compare the safety and efficacy of VS002A against the standard WHO-ORS in treating non-cholera acute watery diarrhoea in children.

Methods

A triple-blind, randomized trial enrolled 310 male infants and children aged 6-36 months, who were assigned to receive WHO-ORS or VS002A over a 16-month period, from June 2021 to September 2022. Both groups received standard of care, including zinc supplementation. The Primary study outcome measured was the duration of diarrhoea. Secondary outcomes included stool output, treatment failure and adverse events. Exploratory endpoints included urinary output, body weight changes, blood biochemistry, stool microbiology and gut health biomarkers.

Findings

Both VS002A and WHO-ORS were well-tolerated with a low adverse event rate. While not different statistically (p = 0.10), duration of diarrhoea was shorter in children treated with VS002A vs. WHO-ORS (65.4 h vs. 72.6 h). Similarly, stool output was also lower vs. WHO-ORS in children treated with VS002A, though not statistically different (p = 0.40). Serum citrulline levels, an indicator of gut health, were higher in the VS002A group at 24 h suggesting a potential protective effect (p = 0.06).

Interpretation

The findings of this study support the non-inferiority of VS002A, a glucose-free amino acid-based ORS compared to the WHO-ORS standard of care. VS002A was shown to be safe and effective in treating non-cholera acute watery diarrhoea in young children. VS002A may offer advantages in pathogen-driven diarrhoea, supported by trends toward a lower duration of diarrhoea and stool output within the per protocol group. Furthermore, individuals with prolonged diarrhoea, severe malnutrition, environmental enteric dysfunction or have issues with obesity or insulin resistance, could benefit from a glucose-free ORS. This research contributes to addressing the persistent challenge of childhood diarrhoea by presenting an alternative glucose-free ORS formulation with potential advantages in select scenarios, offering a promising avenue for improving paediatric diarrhoea management worldwide.

Funding

The study was funded by Entrinsic Bioscience, LLC., Norwood, MA, USA.

Changes in porcine nutrient transport physiology in response to Ascaris suum infection

Background

The roundworm Ascaris suum is one of the parasites with the greatest economic impact on pig farming. In this context, lower weight gain is hypothesized to be due to decreased nutrient absorption. This study aims at characterizing the effects of A. suum infection on intestinal nutrient transport processes and potential molecular mechanisms.

Methods

Three groups of six piglets each were infected orally (10,000 embryonated A. suum eggs) in a single dose (“single infection”). Another three groups were infected orally (1000 embryonated eggs) for 10 consecutive days (“trickle infection”). Animals were necropsied 21, 35 and 49 days post-infection (dpi). Three groups served as respective controls. The Ussing chamber technique was applied for the functional characterization of small intestinal tissues [short-circuit currents (I_sc) as induced by glucose, alanine and peptides; ³H-glucose net flux rates; tissue conductance (G_t)]. Transcription and expression levels of relevant cytokines and nutrient transporters were evaluated (qPCR/western blot).

Results

Peptide- and alanine-induced changes in I_sc were significantly decreased in the jejunum and ileum of the trickle-infected group at 49 dpi and in the ileum of the single-infected group at 49 dpi. No significant differences regarding glucose transport were observed between the Ascaris-infected groups and the control group in Ussing chamber experiments. Transcription levels of the glucose and peptide transporters as well as of selected transcription factors (transcription of signal transducer and activator of transcription 6 [STAT6] and hypoxia-inducible factor 1-alpha [Hif-1α]) were significantly increased in response to both infection types after some periods. The transcription of interleukins 4 and 13 varied between decrease and increase regarding the respective time points, as did the protein expression of glucose transporters. The expression of the peptide transporter PepT1 was significantly decreased in the ileal single-infected group at 35 dpi. Hif-1α was significantly increased in the ileal tissue from the single-infected group at 21 dpi and in the trickle-infected group at 35 dpi. The expression levels of Na⁺/K⁺-ATPase and ASCT1 remained unaffected.

Conclusions

In contrast to the current hypothesis, these results indicate that the nutrient deprivation induced by A. suum cannot be explained by transcriptional or expression changes alone and requires further studies.

Graphical abstract

Are oral rehydration solutions optimized for treating diarrhea?

BACKGROUND

A historical turning point occurred in the treatment of diarrhea when it was discovered that glucose could enhance intestinal sodium and water absorption. Adding glucose to salt water (oral rehydration solution, ORS) more efficiently replaced intestinal water and salt losses.

AIM

Provide a novel hypothesis to explain why mainstream use of ORS has been strongly recommended, but weakly adopted.

METHODS

Traditional (absorptive) and novel (secretory) physiological functions of glucose in an ORS were reviewed.

RESULTS

Small amounts of glucose can stimulate both intestinal absorption and secretion. Glucose can exacerbate a net secretory state and may aggravate pathogen-induced diarrhea, particularly for pathogens that affect glucose transport.

CONCLUSION

A hypothesis is made to explain why glucose-based ORS does not appreciably reduce diarrheal stool volume and why modern food science initiatives should focus on ORS formulations that replace water and electrolytes while also reducing stool volume and duration of diarrhea.

Osmolality of Commercially Available Oral Rehydration Solutions: Impact of Brand, Storage Time, and Temperature

Oral rehydration solutions (ORS) are specifically formulated with an osmolality to optimize fluid absorption. However, it is unclear how many ORS products comply with current World Health Organization (WHO) osmolality guidelines and the osmotic shelf-life stability is not known. Therefore, the purpose of this investigation was to examine the within and between ORS product osmolality variation in both pre-mixed and reconstituted powders. Additionally, the osmotic stability was examined over time. The osmolality of five different pre-mixed solutions and six powdered ORS products were measured. Pre-mixed solutions were stored at room temperatures and elevated temperatures (31 °C) for two months to examine osmotic shelf stability. Results demonstrated that only one pre-mixed ORS product was in compliance with the current guidelines both before and after the prolonged storage. Five of the six powdered ORS products were in compliance with minimal inter-packet variation observed within the given formulations. This investigation demonstrates that many commercially available pre-mixed ORS products do not currently adhere to the WHO recommended osmolality guidelines. Additionally, due to the presence of particular sugars and possibly other ingredients, the shelf-life stability of osmolality for certain ORS products may be questioned. These findings should be carefully considered in the design of future ORS products.

Clinical Trial of a Rice-Powder Oral Rehydration Beverage

A clinical trial was conducted to assess the efficacy of a rice-based gruel as a rehydration solution, identified in a previous study to be widely used by mothers during diarrhoeal episodes in their children. Seventy children under five years of age, admitted to a paediatric hospital with clinical dehydration secondary to acute diarrhoea, were randomly assigned to receive rice-based gruel (n = 37) or oral rehydration salts (ORS) (n = 33). The hydration status was measured on admission and hourly until discharge, for a maximum of 8 hours, after which treatment was considered to have failed in children who had not been rehydrated Successful rehydration was achieved in 92% of the patients receiving rice-based gruel and 91% of those receiving ORS. Over 50% of all patients were rehydrated 4 to 5 hours after treatment was initiated; at these times the faecal output was statistically significantly lower in patients receiving rice-based gruel than in those receiving ORS. More patients were discharged from the study with hypernatraemia in the group receiving ORS than in the group receiving rice-based gruel, whereas the number of patients with hyponatraemia on discharge was similar in both groups. Faecal sodium concentrations were similar on admission in both groups but were statistically significantly lower at discharge in the group receiving rice-based gruel. We concluded that rice-based gruel could be safely used as an oral rehydration solution at the community level.

Carriers, exchangers, and cotransporters in the first 100 years of the Journal of General Physiology

Jennings reviews the many contributions of JGP articles to our current understanding of solute transporter mechanisms.

Transporters, pumps, and channels are proteins that catalyze the movement of solutes across membranes. The single-solute carriers, coupled exchangers, and coupled cotransporters that are collectively known as transporters are distinct from conductive ion channels, water channels, and ATP-hydrolyzing pumps. The main conceptual framework for studying transporter mechanisms is the alternating access model, which comprises substrate binding and release events on each side of the permeability barrier and translocation events involving conformational changes between inward-facing and outward-facing conformational states. In 1948, the Journal of General Physiology began to publish work that focused on the erythrocyte glucose transporter—the first transporter to be characterized kinetically—followed by articles on the rates, stoichiometries, asymmetries, voltage dependences, and regulation of coupled exchangers and cotransporters beginning in the 1960s. After the dawn of cDNA cloning and sequencing in the 1980s, heterologous expression systems and site-directed mutagenesis allowed identification of the functional roles of specific amino acid residues. In the past two decades, structures of transport proteins have made it possible to propose specific models for transporter function at the molecular level. Here, we review the contribution of JGP articles to our current understanding of solute transporter mechanisms. Whether the topic has been kinetics, energetics, regulation, mutagenesis, or structure-based modeling, a common feature of these articles has been a quantitative, mechanistic approach, leading to lasting insights into the functions of transporters.

Epithelial transport in The Journal of General Physiology

JGP hosts key papers that shaped the epithelial transport field.

Epithelia define the boundaries of the body and often transfer solutes and water from outside to inside (absorption) or from inside to outside (secretion). Those processes involve dual plasma membranes with different transport components that interact with each other. Understanding those functions has entailed breaking down the problem to analyze properties of individual membranes (apical vs. basolateral) and individual transport proteins. It also requires understanding of how those components interact and how they are regulated. This article outlines the modern history of this research as reflected by publications in The Journal of General Physiology.

Regulation of Intestinal Glucose Absorption by Ion Channels and Transporters

The absorption of glucose is electrogenic in the small intestinal epithelium. The major route for the transport of dietary glucose from intestinal lumen into enterocytes is the Na⁺/glucose cotransporter (SGLT1), although glucose transporter type 2 (GLUT2) may also play a role. The membrane potential of small intestinal epithelial cells (IEC) is important to regulate the activity of SGLT1. The maintenance of membrane potential mainly depends on the activities of cation channels and transporters. While the importance of SGLT1 in glucose absorption has been systemically studied in detail, little is currently known about the regulation of SGLT1 activity by cation channels and transporters. A growing line of evidence suggests that cytosolic calcium ([Ca²⁺]_cyt) can regulate the absorption of glucose by adjusting GLUT2 and SGLT1. Moreover, the absorption of glucose and homeostasis of Ca²⁺ in IEC are regulated by cation channels and transporters, such as Ca²⁺ channels, K⁺ channels, Na⁺/Ca²⁺ exchangers, and Na⁺/H⁺ exchangers. In this review, we consider the involvement of these cation channels and transporters in the regulation of glucose uptake in the small intestine. Modulation of them may be a potential strategy for the management of obesity and diabetes.

Oral rehydration therapy in the second decade of the twenty-first century

Oral rehydration solution (ORS) was established as the cornerstone of therapy for dehydration secondary to acute infectious diarrhea approximately 40 years ago. The efficacy of ORS is based on the ability of glucose to stimulate Na and fluid absorption in the small intestine via a cyclic AMP-independent process. Despite the establishment that ORS is the primary reason for the substantial reduction in morbidity and mortality from diarrhea in children in developing countries, the use of ORS has lagged for many reasons. This review highlights efforts to establish a major reformulation of ORS following the demonstration that short-chain fatty acids (SCFA) stimulate colonic Na and fluid absorption by a cyclic AMP-independent mechanism. The addition of high-amylose maize starch (HAMS), a microbially-fermentable (or 'resistant') starch, to ORS results in delivery of non-absorbed carbohydrate to the colon where it is fermented to SCFA. To date, three randomized controlled trials with a HAMS-ORS in south India have demonstrated a substantial decrease in diarrhea duration in both adults and children hospitalized for acute diarrhea. Significant efforts are now underway to establish this dual-action, modified HAMS-hypoosmolar ORS solution as the standard ORS for the treatment of dehydration from acute diarrhea.

Glucose stimulates calcium-activated chloride secretion in small intestinal cells

The sodium-coupled glucose transporter-1 (SGLT1)-based oral rehydration solution (ORS) used in the management of acute diarrhea does not substantially reduce stool output, despite the fact that glucose stimulates the absorption of sodium and water. To explain this phenomenon, we investigated the possibility that glucose might also stimulate anion secretion. Transepithelial electrical measurements and isotope flux measurements in Ussing chambers were used to study the effect of glucose on active chloride and fluid secretion in mouse small intestinal cells and human Caco-2 cells. Confocal fluorescence laser microscopy and immunohistochemistry measured intracellular changes in calcium, sodium-glucose linked transporter, and calcium-activated chloride channel (anoctamin 1) expression. In addition to enhancing active sodium absorption, glucose increased intracellular calcium and stimulated electrogenic chloride secretion. Calcium imaging studies showed increased intracellular calcium when intestinal cells were exposed to glucose. Niflumic acid, but not glibenclamide, inhibited glucose-stimulated chloride secretion in mouse small intestines and in Caco-2 cells. Glucose-stimulated chloride secretion was not seen in ileal tissues incubated with the intracellular calcium chelater BAPTA-AM and the sodium-potassium-2 chloride cotransporter 1 (NKCC1) blocker bumetanide. These observations establish that glucose not only stimulates active Na absorption, a well-established phenomenon, but also induces a Ca-activated chloride secretion. This may explain the failure of glucose-based ORS to markedly reduce stool output in acute diarrhea. These results have immediate potential to improve the treatment outcomes for acute and/or chronic diarrheal diseases by replacing glucose with compounds that do not stimulate chloride secretion.

Glucose transport into everted sacs of the small intestine of mice

The Na(+)-glucose cotransporter is a key transport protein that is responsible for absorbing Na(+) and glucose from the luminal contents of the small intestine and reabsorption by the proximal straight tubule of the nephron. Robert K. Crane originally described the cellular model of absorption of Na(+) and glucose by a "cotransport process" in 1960. Over the past 50+ yr, numerous groups have tested and verified Crane's hypothesis. Eventually, Wright and colleagues cloned the Na(+)-glucose cotransporter (SGLT1; the product of the SLC5A1 gene) in 1987. This article provides a "hands-on" laboratory exercise using the everted mouse jejunal preparation (everted sac) that allows students to investigate various components of the Na(+)-glucose cotransport absorptive cell model (e.g., Na(+) dependence of SGLT1, inhibition of SGLT1, and inhibition of Na(+)-K(+)-ATPase). Additionally, the laboratory exercise includes a case-based study of glucose-galactose malabsorption in which the students conduct an internet search and participate in a small-group discussion during the laboratory period to better understand the basic principles and functions of the Na(+)-glucose absorptive process of the small intestine. This laboratory exercise was introduced into the second-year undergraduate physiology curriculum in 2008, and >850 physiology students have participated in this laboratory exercise. The students have produced very robust and reproducible data that clearly illustrate the theory of the cellular model for Na(+)-glucose absorption by the jejunum.

Robert K. Crane-Na(+)-glucose cotransporter to cure?

Dr. Robert K. Crane made major contributions to our understanding of carbohydrate metabolism and transport of the intestine over a very long and productive career. This Perspective examines, briefly, his early life and academic positions, but more importantly, this Perspective highlights his contributions to the understanding of coupled Na(+)-glucose absorption by the small intestine. I discuss how his early hypothesis of a "cotransport" of sodium and glucose ushered in and provided the physiological explanation for the clinical treatment of acute diarrhea and cholera when using oral rehydration therapy (ORT). ORT saves millions of lives each year. Certainly, humankind is better off because of Crane's hypothesis of the Na(+)-glucose cotransporter that he put forth over 50 years ago?

Sodium-glucose interactions in the goldfish intestine

1. Everted sacs of goldfish intestine transfer glucose and water to their serosal surfaces and the total transfer is greater in the anterior intestine than in the intestinal bulb or rectum.2. Transmural potentials, with the serosa positive to the mucosa, were recorded from all parts of the goldfish intestine but were highest in the anterior intestine and the rectum. In both these areas the total potential was dependent partly upon the presence of glucose.3. Reducing the concentration of sodium bathing the mucosa of the anterior intestine reduced the glucose-evoked potential in a non-linear way. The steady-state potentials, with or without glucose, first increased and later decreased as the sodium concentration was further reduced.4. Reducing the concentration of glucose bathing the mucosa from 27 to 5 mM slightly increased the glucose-evoked potential. Further reduction of the glucose concentration caused the glucose-evoked potential to fall.5. Phlorrhizin inhibited the glucose-evoked potential. The degree of inhibition was proportional to the log concentration of phlorrhizin over the range 2 x 10(-7)-6 x 10(-5)M. The steady-state potential with glucose present was lower than when glucose was absent at phlorrhizin concentrations, 6 x 10(-6)-6 x 10(-5)M.6. The glucose-evoked potential increased rapidly over the temperature range 5-15 degrees C and more slowly from 15 to 30 degrees C. The steady-state potentials also increased with temperature, the rate of increase being greater when glucose was present. Below 15 degrees C the glucose-independent potential was higher and above 15 degrees C lower than the steady-state potential recorded with glucose present.7. These findings are discussed in terms of sodium-glucose interaction taking place at the luminal side of the mucosal cell, on the outside of the mucosal cell membrane.

The origin of the glucose dependent increase in the potential difference across the tortoise small intestine

1. Experiments were carried out to investigate the origin of the glucose dependent increase in the potential difference (p.d.) across the isolated intestinal mucosa of the tortoise.2. In addition to glucose, galactose, alpha-methyl glucoside, 3-0-methyl glucopyranose and sucrose also increased the transepithelial potential difference. There was no increase with either fructose or mannose.3. The use of micro-electrodes demonstrated that the change in the p.d. due to the presence of glucose was wholly accounted for by the increase in the p.d. across the serosal face of the epithelial cells.4. Diffusion potentials were produced across the isolated mucosa by varying the ionic composition of either the mucosal or serosal fluids. However, there was no reduction of the glucose dependent increase in the p.d. when the ionic concentration gradients across the serosal face of the cell were reversed.5. These results suggest that the increase in the p.d. associated with the active transfer of sugars across the small intestine was due to the presence of an electrogenic ion pump at the serosal face of the epithelial cell.

The effect of oral rehydration solution and recommended home fluids on diarrhoea mortality

Background Most diarrhoeal deaths can be prevented through the prevention and treatment of dehydration. Oral rehydration solution (ORS) and recommended home fluids (RHFs) have been recommended since 1970s and 1980s to prevent and treat diarrhoeal dehydration. We sought to estimate the effects of these interventions on diarrhoea mortality in children aged <5 years.

Methods We conducted a systematic review to identify studies evaluating the efficacy and effectiveness of ORS and RHFs and abstracted study characteristics and outcome measures into standardized tables. We categorized the evidence by intervention and outcome, conducted meta-analyses for all outcomes with two or more data points and graded the quality of the evidence supporting each outcome. The CHERG Rules for Evidence Review were used to estimate the effectiveness of ORS and RHFs against diarrhoea mortality.

Results We identified 205 papers for abstraction, of which 157 were included in the meta-analyses of ORS outcomes and 12 were included in the meta-analyses of RHF outcomes. We estimated that ORS may prevent 93% of diarrhoea deaths.

Conclusions ORS is effective against diarrhoea mortality in home, community and facility settings; however, there is insufficient evidence to estimate the effectiveness of RHFs against diarrhoea mortality.

Lactose intolerance in infants with gluten-sensitive enteropathy: Frequency and clinical characteristics

Introduction. Secondary lactose intolerance (SLI) belongs to the rarer manifestations of gluten-sensitive enteropathy (GSE). It occurs in more severe forms of the disease and its presence contributes significantly to the degree of its expression. Objective. The goal of the study was to determine the frequency of SLI in infants with clinically classic form of GSE, as well as its relationship with the duration, severity and age at the diagnosis of the basic disease and the degree of small bowel mucosa damage. Methods. The study was based on a sample of 42 infants, 30 female and 12 male, aged 7-12 months (x=9.98?1.69), with a clinically classic form of GSE. The diagnosis of GSE was established based on the characteristic pathohistological appearance of small bowel mucosa and clinical improvement of patients on gluten-free diet, while SLI on pathological lactose or milk tolerance test. The assessment of basic disease severity was based on body mass divergence in relation to the standard value, as well as on Hb and serum iron levels, while the degree of small bowel mucosa damage was determined according to the modified Marsh criteria. Results. SLI was verified in 8/42 or 19.05% of patients. In addition to the symptoms and clinical signs of GSE, all the patients with SLI also featured the problems characteristic of lactose tolerance disorders, i.e. watery diarrhoea, borborygmus and meteorism occurring after milk meals. In addition, all had perianal erythema (6 with erosive changes), as well as destructive enteropathy (5 subtotal and 3 total). The difference in the duration of the basic disease, age at diagnosis, as well as in the degree of body mass deviation from the standard value between the lactose-tolerant and lactose-intolerant infants was not found. In addition, no difference in Hb and serum iron levels or in the degree of small bowel mucosa damage was found between the two groups. Conclusion. Our findings indicate that SLI presents a relatively frequent occurrence in infants with clinically classic GSE, as well as that it occurs independently to the duration, severity and age at diagnosis of the basic disease and the degree of small bowel mucosa damage.

1,25-dihydroxyvitamin D(3) rapidly stimulates the solvent drag-induced paracellular calcium transport in the duodenum of female rats

A calcium-regulating hormone 1alpha,25-dihydroxyvitamin D(3) (1,25-[OH](2)D(3)) has been known to rapidly stimulate the transcellular active calcium transport in the chick duodenum. However, its effects on the solvent drag-induced paracellular calcium transport, which normally contributes approximately 70% of the total active calcium transport, and the underlying mechanism were unknown. The present study aimed to investigate the rapid nongenomic actions of physiological concentrations of 1,25-(OH)(2)D(3), i.e., 1, 10, and 100 nmol/l, on the duodenal calcium absorption in female rats. Quantitative real-time PCR revealed strong expressions of the classical vitamin D receptor (VDR) and the membrane-associated rapid response steroid binding receptors (MARRS) in both small and large intestines. By using the Ussing chamber technique, we found that duodenal epithelia acutely exposed to 10 and 100 nmol/l 1,25-(OH)(2)D(3) rapidly increased the solvent drag-induced calcium transport, but not the transcellular calcium transport, in a dose-response manner. On the other hand, 3-day daily injections of 1,25-(OH)(2)D(3) enhanced the transcellular active duodenal calcium transport. The 1,25-(OH)(2)D(3)-stimulated solvent drag-induced transport was abolished by the phosphatidylinositol 3-kinase (PI3K) inhibitors, 200 nmol/l wortmannin and 75 micromol/l LY294002, as well as PKC (1 micromol/l GF109203X) and MEK inhibitors (10 micromol/l U0126). Although 100 nmol/l 1,25-(OH)(2)D(3) did not alter the transepithelial mannitol flux, indicating no widening of the tight junction, it decreased the transepithelial resistance and increased both sodium and chloride permeability through the paracellular channel. We conclude that 1,25-(OH)(2)D(3) uses the nongenomic signaling pathways involving PI3K, PKC, and MEK to rapidly enhance the solvent drag-induced calcium transport, partly by altering the charge-selective property of the duodenal epithelium at least for the pathways involving PI3K and MEK.

Taking science where the diarrhoea is

With attack rates exceeding two episodes per year in the young diarrhoea with attendant dehydration is by far the major single killer in the developing world. An invariable accompaniment of the more insidious and chronic protein-energy malnutrition (PEM), diarrhoea is itself an acute form of malnutrition: fluid-electrolyte malnutrition (FEM). Scientific attention to FEM has focused heavily on mechanisms of pathogenesis and disordered physiology, often to the neglect of preventive and effective control measures. A notable exception was the huge step from the short-circuit chamber to the cholera ward which carried the science of coupled transport to the field. Glucose-electrolyte solutions provide effective prevention and treatment of dehydration and, where combined with early proper feeding, an interruption of the FEM-PEM cycle. Wider use of this simple technology awaits greater understanding and interact-on with the social systems that determine the ecology of diarrhoeal disease.

Gastrointestinal Function

This chapter describes the normal biochemical processes of intestinal secretion, digestion, and absorption. The digestive system is composed of the gastrointestinal (GI) tract, or the alimentary canal, salivary glands, the liver, and the exocrine pancreas. The principal functions of the gastrointestinal tract are to digest and absorb ingested nutrients, and to excrete waste products of digestion. Most nutrients are ingested in a form that is either too complex for absorption or insoluble, and therefore, indigestible or incapable of being digested. Within the GI tract, much of these substances are solubilized and further degraded enzymatically to simple molecules, sufficiently small in size, and in a form that permits absorption across the mucosal epithelium. This chapter explains in detail the mechanisms of salivary secretions, compositions of saliva, and the functions of saliva. The chapter also elaborates properties of bile as well as the synthesis of bile acids. The chapter explores the pathogenesis of the important gastrointestinal diseases of domestic animals, and the biochemical basis for their diagnosis and treatment. The chapter concludes with a discussion on disturbances of gastrointestinal function such as vomition, acute diarrheas, malabsorption, bacterial overgrowth, and ulcerative colitis.

From a pump handle to oral rehydration therapy: a model of translational research

Few afflictions have attracted as much attention and impacted on as many societal and biomedical areas as cholera. Dr. John Snow's studies launched the field of epidemiology, were early applications of medical cartography, and promoted the use of statistical methods in medicine. The finding that cholera was due to the ingestion of contaminated water lent to the demise of the prevalent "miasmatic theory of contagion," set the platform for the "germ theory of disease," and promoted the growth of public health concerns for water purification and sanitation. More recent attention to this disease led to the notion of "secretory diarrhea" and the translation of basic principles to the development of oral rehydration therapy and its "spin-offs" (Gatorade and Pedilyte).

H+-coupled nutrient, micronutrient and drug transporters in the mammalian small intestine

The H(+)-electrochemical gradient was originally considered as a driving force for solute transport only across cellular membranes of bacteria, plants and yeast. However, in the mammalian small intestine, a H(+)-electrochemical gradient is present at the epithelial brush-border membrane in the form of an acid microclimate. Over recent years, a large number of H(+)-coupled cotransport mechanisms have been identified at the luminal membrane of the mammalian small intestine. These transporters are responsible for the initial stage in absorption of a remarkable variety of essential and non-essential nutrients and micronutrients, including protein digestion products (di/tripeptides and amino acids), vitamins, short-chain fatty acids and divalent metal ions. Proton-coupled cotransporters expressed at the mammalian small intestinal brush-border membrane include: the di/tripeptide transporter PepT1 (SLC15A1); the proton-coupled amino-acid transporter PAT1 (SLC36A1); the divalent metal transporter DMT1 (SLC11A2); the organic anion transporting polypeptide OATP2B1 (SLC02B1); the monocarboxylate transporter MCT1 (SLC16A1); the proton-coupled folate transporter PCFT (SLC46A1); the sodium-glucose linked cotransporter SGLT1 (SLC5A1); and the excitatory amino acid carrier EAAC1 (SLC1A1). Emerging research demonstrates that the optimal intestinal absorptive capacity of certain H(+)-coupled cotransporters (PepT1 and PAT1) is dependent upon function of the brush-border Na(+)-H(+) exchanger NHE3 (SLC9A3). The high oral bioavailability of a large number of pharmaceutical compounds results, in part, from absorptive transport via the same H(+)-coupled cotransporters. Drugs undergoing H(+)-coupled cotransport across the intestinal brush-border membrane include those used to treat bacterial infections, hypercholesterolaemia, hypertension, hyperglycaemia, viral infections, allergies, epilepsy, schizophrenia, rheumatoid arthritis and cancer.

Review article: the history of acute infectious diarrhoea management--from poorly focused empiricism to fluid therapy and modern pharmacotherapy

BACKGROUND

Acute diarrhoea management has progressed from largely ineffective measures in the early years to a more effective physiologic approach in recent years.

AIM

To review the history of acute diarrhoea management.

METHODS

Citations in PubMed were reviewed on 'acute diarrhoea treatment' along with an extensive file maintained by the corresponding author.

RESULTS

Freedom from diarrhoea was equated in early military conflicts with bravery and strength where diarrhoea-free soldiers had the 'guts' to fight. Until early 20th century, colonic irrigants, purgatives and emetic drugs were used to help eliminate undesired intestinal contents. Only a few early authorities suggested the need for replacement of fluids and salt, now standard treatment. Drugs aimed at diarrhoea symptom control have been broadly used for more than 100 years. The evolving history of one of those drugs, kaopectate is unappreciated. Once understanding the pathophysiology and infectious aetiology of acute diarrhoea, new oral fluids, pharmacologic agents designed to block specific secretory alterations and anti-infective drugs have been identified.

CONCLUSIONS

Physiologic and antimicrobial approaches to controlling diarrhoea can lead to reduction of stool number and enteric complaints, important in industrialized areas, with the potential for decreasing threat of fatal illness among infants in developing regions.

Reduced oxygen concentration improves the developmental competence of mouse oocytes following in vitro maturation

Reduced atmospheric oxygen concentration is beneficial to embryo development; however, optimal oxygen concentration for oocyte maturation remains undetermined. Likewise, there is no consensus of appropriate medium supplementation during maturation. The objective of this study was to determine whether oxygen tension (20% or 5% O2) and epidermal growth factor (EGF) affect oocyte metabolism and subsequent embryo development. Cumulus-oocyte complexes (COCs) were collected from 28-day-old equine chorionic gonadotropin (eCG) primed or unprimed F1 (C57BL/6xCBA) mice. COCs were matured in defined medium in one of four groups: 20% O2, 20% O2 + EGF, 5% O2, 5% O2 + EGF. In vivo matured COCs were also collected for analysis. COCs from unprimed mice, matured in 5% O2 +/- EGF or 20% O2 + EGF had higher metabolic rates than COCs matured in 20% O2 (P < 0.05). COCs from primed mice had higher metabolic rates when matured in the presence of EGF, regardless of oxygen tension (P < 0.01). Oxygen uptake and mitochondrial membrane potential were higher for in vivo matured oocytes and oocytes matured under 5% O2 compared to oocytes matured under 20% O2 (P < 0.05). Blastocyst formation was not different between maturation groups (primed or unprimed); however, embryo cell numbers were 20-45% significantly higher when COCs were matured at 5% O2 (P < 0.05). Results suggest that oocytes matured in physiological concentrations of oxygen have improved development and metabolic activity, more closely resembling in vivo maturation. These findings have implications for oocyte maturation in both clinical and research laboratories.

Disease-associated mutations affect intracellular traffic and paracellular Mg2+ transport function of Claudin-16

Claudin-16 (Cldn16) is selectively expressed at tight junctions (TJs) of renal epithelial cells of the thick ascending limb of Henle's loop, where it plays a central role in the reabsorption of divalent cations. Over 20 different mutations in the CLDN16 gene have been identified in patients with familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC), a disease of excessive renal Mg2+ and Ca2+ excretion. Here we show that disease-causing mutations can lead to the intracellular retention of Cldn16 or affect its capacity to facilitate paracellular Mg2+ transport. Nine of the 21 Cldn16 mutants we characterized were retained in the endoplasmic reticulum, where they underwent proteasomal degradation. Three mutants accumulated in the Golgi complex. Two mutants were efficiently delivered to lysosomes, one via clathrin-mediated endocytosis following transport to the cell surface and the other without appearing on the plasma membrane. The remaining 7 mutants localized to TJs, and 4 were found to be defective in paracellular Mg2+ transport. We demonstrate that pharmacological chaperones rescued surface expression of several retained Cldn16 mutants. We conclude that FHHNC can result from mutations in Cldn16 that affect intracellular trafficking or paracellular Mg2+ permeability. Knowledge of the molecular defects associated with disease-causing Cldn16 mutations may open new venues for therapeutic intervention.

A legacy in 20th-century medicine: Robert Allan Phillips and the taming of cholera

The legacy of Captain Robert Allan Phillips (1906-1976) was to establish effective, evidence-based rehydration methods for the treatment of cholera. As a Navy Lieutenant at the Rockefeller Institute for Medical Research (New York, New York) during World War II, Phillips developed a field method for the rapid assessment of fluid loss in wounded servicemen. After the war, he championed the establishment of United States Naval Medical Research Unit (NAMRU)-3 (Cairo; 1946) and NAMRU-2 (Taipei; 1955), serving at the helm of both units. Phillips embarked on cholera studies during the 1947 Egyptian cholera epidemic and brought them to maturity at NAMRU-2 (1958-1965), elucidating the pathophysiologic derangements induced by cholera and developing highly efficacious methods of intravenous rehydration. His conception of a simpler cholera treatment was realized in the late 1960s with the development of glucose-based oral rehydration therapy, a monumental breakthrough to which many other investigators made vital contributions. Today, these simple advances have been integrated into everyday medical practice across the globe, saving millions of lives annually.

Impairment of epithelial transport but not of barrier function in idiopathic pouchitis after ulcerative colitis

BACKGROUND AND AIMS

Little is known of the permeability of ileoanal pouches. Hence the aim of the present study was to determine changes in permeability and mucosal function after ileo-pouchanal anastomosis (IPAA) in patients with ulcerative colitis.

MATERIALS AND METHODS

Biopsies were taken from 43 patients (male:female ratio 28:15; mean age 35.2 (12.5) years) prior to colectomy (ileum prior to pouch), prior to closure of ileostomy (deviation), and after closure of ileostomy (intact pouch) in the case of pouchitis, and from 14 healthy controls. Tissues were mounted in a miniaturised Ussing chamber. Epithelial and subepithelial resistance was determined by transmural impedance analysis. Active Na(+)-glucose cotransport was measured as change in short circuit current after stepwise addition of glucose, and active Cl(-) secretion was measured after stimulation with theophylline and prostaglandin E(2).

RESULTS

Neither epithelial resistance nor mannitol fluxes were significantly altered compared with intact controls, indicating no barrier defect in pouchitis. Subepithelial resistances of intact pouches and pouchitis were increased compared with deviation (18.2 (1.6) and 24.3 (1.5) v. 13.6 (1.0) Omegaxcm(2)) consistent with an adaptive thickening of the subepithelial layer. In contrast, active Cl(-) secretion of pouchitis tissues was reduced versus intact pouch and controls (1.4 (0.3) v. 4.3 (0.7) and 4.6 (0.7) micromol/h/cm(2)), and Na(+)-glucose cotransport of pouchitis was reduced compared with intact pouch and controls (1.8 (0.5) v. 4.2 (0.8) and 8.8 (1.3) micromol/h/cm(2)).

CONCLUSIONS

Ileal mucosa in pouchitis and terminal ileum prior to IPAA exhibit impaired secretory and absorptive transport functions whereas the epithelial barrier function remains unchanged. This differs from findings in ulcerative colitis. Thus the hypothesis that pouchitis represents a remanifestation of ulcerative colitis has to be questioned.

Taurocholic acid-induced secretion in normal and cystic fibrosis mouse ileum

Bile acids cause secretion throughout the intestinal tract and this process contributes to maintaining the fluidity of intestinal contents. In cystic fibrosis (CF) defective intestinal secretion can lead to excessive dehydration of the luminal contents and the development of clinical symptoms. This study was designed to investigate bile acid-induced secretion in mouse ileum and to determine whether this process was defective in CF. Taurocholic acid-induced secretion was monitored as a rise in short-circuit current (SCC) in ileal sheets from normal (Swiss MF1) and transgenic CF mice. Taurocholic acid increased the SCC in both intact and stripped ileal sheets from Swiss MF1 mice. This effect was due to a stimulation of electrogenic Cl- secretion as it was inhibited by Cl(-)-free conditions, serosal furosemide (frusemide), mucosal diphenylamine-2-carboxylic acid (DPC) and increased serosal K+ concentration, without being affected by reduced mucosal Na+ concentration. Taurocholic acid-induced secretion was inhibited by tetrodotoxin, indicating the involvement of a neural pathway, but this did not include capsaicin-sensitive afferent neurons or muscarinic cholinoreceptors. Mucosal mast cells also contributed to the response. Responses in tissues from transgenic wild-type mice were similar to those obtained with Swiss MF1 animals, but ilea from CF mice exhibited a lower basal SCC with significantly reduced secretory responses to acetylcholine and taurocholic acid. We concluded that taurocholic acid induces ileal secretion by a mechanism that entails activation of enteric nerves and degranulation of mucosal mast cells. Impaired bile acid-induced secretion in CF may contribute to luminal dehydration.

Fifty landmark discoveries in gastroenterology during the past 50 years. A brief history of modern gastroenterology at the millennium: Part I. Gastrointestinal procedures and upper gastrointestinal disorders

During the last half century, many outstanding discoverers have revolutionized the clinical practice and science of gastroenterology. Whereas the scientific results are widely disseminated, the discoverers have received inadequate recognition, and the history of their discoveries is poorly known. At the millennium, a committee selected the 50 landmark discoveries in gastroenterology during the past 50 years. A brief history of each landmark discovery is presented. Part I presents the landmark discoveries in gastrointestinal (GI) procedures and in upper GI disorders. Part II of this presentation, which covers landmark discoveries in other areas of gastroenterology, will publish in Part II of the volume on High Risk Gastrointestinal Bleeding.

Efficacy of a glutamine-based oral rehydration solution on the electrolyte and water absorption in a rabbit model of secretory diarrhea induced by cholera toxin

BACKGROUND

Glutamine is absorbed in the intestinal tract coupled with sodium and is the principal metabolic substrate for the enterocyte. Therefore, an oral rehydration solution containing this substance might provide an effective oral means of restoring electrolyte losses as well as speeding repair of mucosal damage. The objective of this work was to investigate the use of an oral rehydration solution based on glutamine in vivo in the perfused rabbit ileal loop model of secretory diarrhea induced by choleratoxin.

METHODS

Phenolsulfonphthalein (PSP, 50 mg/l) was used as a nonabsorbable marker for calculations of net water and electrolyte transport. Solutions tested included: (a) a glutamine-based oral rehydration solution with 111 mmol/l glutamine, (Gln-ORS); (b) the oral rehydration solution recommended by the World Health Organization; (c) modified Ringer's solution. Choleratoxin (1 microg/ml) was injected into the lumen of the ileal rabbit segments for 30 minutes prior to the initiation of the perfusion.

RESULTS

Choleratoxin induced significant secretion of sodium in the control modified Ringer's solution (10.8 +/- 2.95 vs -14.05 +/- 5.95 microEq/g/min, n = 10; p < 0.01) and of water (0.06 +/- 0.03 vs -0.15 +/- 0.06 ml/g/min, n = 10; p < 0.01) with a maximum effect at 60 minutes after initiation of perfusion. World Health Organization oral rehydration solution was able to significantly reduce the intestinal secretion of sodium (control with cholera = -14.34 +/- 2.18 vs oral rehydration solution with cholera = -0.50 +/- 0.48 microEq/g/min, n = 10; p < 0.01) and water (-0.15 +/- 0.02 vs -0.012 +/- 0.005 ml/g/min, n = 10; p < 0.01). For comparison, glutamine-based oral rehydration solution had an even greater effect on sodium and water absorption (glutamine-based oral rehydration solution with choleratoxin = 10.31 +/- 1.21 microEq/g/min, n = 5; p < 0.01 for sodium and 0.08 +/- 0.008 ml water/g/min; n = 5; p < 0.01). Choleratoxin did not change the effect of glutamine-based oral rehydration solution on sodium and water absorption (12.90 +/- -1.09 microEq sodium/g/min, n = 5; and 0.11 +/- 0.01 ml water/g/min; n = 5). In addition glutamine-based oral rehydration solution also induced a greater absorption of potassium and chloride in the intestinal ileal segments treated with choleratoxin compared with World Health Organization glutamine-based oral rehydration solution.

CONCLUSIONS

These results demonstrate the superior efficacy of glutamine-based oral rehydration solution in electrolyte and water absorption compared with modified Ringer's control solution or even with World Health Organization-recommended oral rehydration solution.

Cytochemical evidence for potassium-dependent p-nitrophenylphosphatase activity in pavement cells of Rana esculenta mesentery

BACKGROUND

We previously reported that during hibernation in Rana esculenta, various organs (i.e., skin, urinary bladder, kidney) change their osmoregulatory activity. Here, we considered the possible role of the frog mesentery in the ion transport, evaluating morphological and cytochemical (K+-p-nitrophenylphosphatase activity) aspects.

METHODS

Pieces of mesentery from Rana esculenta collected in their natural environment during April, June, October, and January were processed to reveal ultrastructural morphology and K+-p-NPPase activity, using cerium as capture agent.

RESULTS

The mesenteric mesothelium contained three types of cells: pavement, mitochondria-rich, and ciliated. Only the pavement cells expressed intense reactivity on the basolateral membranes and in the adjacent pinocytotic vesicles; some reaction product also was found on the apical membranes. Moreover, morphological and cytochemical characteristics of the pavement cells appeared to be very seasonal.

CONCLUSIONS

The presence of mitochondria-rich cells and ciliated cells, generally found in structures involved in the transport of liquids, as well as K+-p-NPPase activity and pinocytosis in pavement cells, is consistent with the hypothesis that frog mesentery may be involved in seasonally variable osmoregulation.

A century of (epithelial) transport physiology: from vitalism to molecular cloning

During the past century, the generally accepted view of the function of biological membranes has evolved from that of a static, inert lipoprotein envelope that simply separates the intracellular machinery from the outside milieu, to that of a dynamic structure that is, in fact, an integral part of that machinery actively involved in homeostasis and bioenergetics. This brief review traces that paradigm shift with special emphasis on the evolution of central concepts in epithelial transport physiology.

Oral rehydration therapy for diarrhea: an example of reverse transfer of technology

On November 13 and 14, 1996, a scientific symposium on oral rehydration therapy (ORT) was held at the Johns Hopkins University School of Hygiene and Public Health in Baltimore, MD. The purpose of the meeting was to review the current treatment practices for the treatment of this disease in the United States. The group noted that diarrhea resulted in 300 to 400 deaths per year among children, approximately 200 000 hospitalizations, 1.5 million outpatient visits, and costs >$1 billion in direct medical costs. ORT is well established therapy for the treatment and prevention of dehydration due to diarrhea. The principles of ORT treatment include early adequate rehydration therapy using an appropriate oral rehydration solution (ORS), replacement of ongoing fluid losses from vomiting and diarrhea with ORS, and frequent feeding of appropriate foods as soon as dehydration is corrected. The effective use of ORT has saved millions of lives around the world. However, in the United States, ORT is grossly underused. Contrary to the recommendations of the American Academy of Pediatrics (AAP) and the Centers for Disease Control and Prevention (CDC), health care providers overuse intravenous hydration, prolong rehydration, delay reintroduction of feeding, and inappropriately withhold ORT, especially with children who are vomiting. The expert panel noted that the majority of deaths, hospitalization, and visits to emergency departments could be prevented by the appropriate use of ORT. They generated guidelines for the treatment and prevention of dehydration secondary to diarrhea. These measures, together with training providers, could substantially reduce diarrhea mortality and decrease hospitalizations of children by 100 000 per year in the next 5 years.

ION TRANSPORT IN ISOLATED RABBIT ILEUM. 3. CHLORIDE FLUXES

Unidirectional Cl fluxes across in vitro segments of rabbit ileum have been determined both in the absence and in the presence of an electrochemical potential gradient. The results indicate that Cl transport in this preparation can be attributed to purely passive forces uninfluenced by solvent drag or exchange diffusion. Furthermore, on the basis of this and previous studies, it has been demonstrated that the sum of the partial ionic conductances of Na and Cl accounts for at least 90 per cent of the total tissue conductance.

Electrolyte fluxes in the gut and oral rehydration solutions

This article provides a brief overview of the normal physiology of water and electrolyte fluxes across the gut as a prerequisite for understanding the pathologic disturbances occurring with diarrheal illnesses. In turn, the rationale for the use of oral rehydration solutions in diarrheal disorders is explored.