The diarrhoea of famine and severe malnutrition--is glucagon the major culprit?

Calcimimetic acts on enteric neuronal CaSR to reverse cholera toxin-induced intestinal electrolyte secretion

Treatment of acute secretory diarrheal illnesses remains a global challenge. Enterotoxins produce secretion through direct epithelial action and indirectly by activating enteric nervous system (ENS). Using a microperfused colonic crypt technique, we have previously shown that R568, a calcimimetic that activates the calcium-sensing receptor (CaSR), can act on intestinal epithelium and reverse cholera toxin-induced fluid secretion. In the present study, using the Ussing chamber technique in conjunction with a tissue-specific knockout approach, we show that the effects of cholera toxin and CaSR agonists on electrolyte secretion by the intestine can also be attributed to opposing actions of the toxin and CaSR on the activity of the ENS. Our results suggest that targeting intestinal CaSR might represent a previously undescribed new approach for treating secretory diarrheal diseases and other conditions with ENS over-activation.

Intestinal transport during fasting and malnutrition

Fasting or malnutrition (FM) has dramatic effects on small intestinal mucosal structure and transport function. Intestinal secretion of ions and fluid is increased by FM both under basal conditions and in response to secretory agonists. Intestinal permeability to ions and macromolecules may also be elevated by FM, which increases the potential for fluid and electrolyte losses and for anaphylactic responses to luminal antigens. Mucosal atrophy induced by FM reduces total intestinal absorption of nutrients, but nutrient absorption normalized to mucosal mass may actually be enhanced by a variety of mechanisms, including increased transporter gene expression, electrochemical gradients, and ratio of mature to immature cells. These observations underscore the value of enteral feeding during health and disease.

Evaluation of a glutamine-containing oral rehydration solution for the treatment of calf diarrhoea using an Escherichia coli model

A high-calorie oral rehydration solution (ORS) with glutamine (n=11) was more effective in correcting plasma, extracellular fluid and blood volume than solutions without (one WHO-type solution, n=6, and two high-glucose but glutamine-free solutions, n=7, n=12). It was the only solution to improve plasma volume significantly within 48 h and sustain the improvement throughout treatment; similarly, it was the only solution to correct packed-cell volume within 48 h and sustain the benefit to the end of treatment. At the end of treatment, the glutamine-treated calves were the only ones to avoid a significant weight loss compared with their pre-diarrhoeic values. The crucial difference between this solution and those used with glutamine previously is that it gave significant nutritional support whereas WHO type solutions did not. It also had more favourable effects on hyponatraemia and metabolic acidosis than a standard ORS. Use of a high-calorie ORS for 4 days (rather than 2 days of 50:50 admixture with milk replacer) brought additional beneficial effects on blood glucose and body weight.

Gluconeogenesis in the livers of diet-restricted rats--a 13C nuclear magnetic resonance study

BACKGROUND

Gluconeogenic activity is reduced during starvation. However, it is less clear whether the utilization of gluconeogenic substrates is diminished with mild but prolonged diet restriction and, if so, whether there are intrinsic changes in the gluconeogenic pathway. We examined gluconeogenesis in the livers of diet-restricted rats with 13C nuclear magnetic resonance (NMR) spectroscopy.

METHODS

Fischer 344 rats were given 88% (DR group) of what was consumed by the weight-matched ad libitum-fed normal rats (CL group). At the end of 5 weeks, the removed livers were perfused with [3-13C] alanine while 13C NMR spectroscopy was performed.

RESULTS

The final body and liver weights were the same for the two groups. In DR rats, both intrahepatic [3-13C] alanine and metabolites generated via pyruvate and oxaloacetate, including aspartate and carbamoyl aspartate, appeared in significantly reduced amounts. There was also marked diminution in the production of glucose.

CONCLUSIONS

In the livers of DR rats, alanine uptake through System A transport, the fluxes through pyruvate carboxylase, the biosynthesis of pyrimidine nucleotides, and the production of glucose from alanine were all significantly decreased with mild intake restriction. Attenuated protein synthesis in the liver of diet-restricted animals may be the cause for this decreased utilization of alanine for gluconeogenesis.

Role of the enteric nervous system in the maintained hypersecretion induced by enterotoxin STa in the nutritionally deprived intestine

Electrogenic (Cl-) secretion was measured as the short circuit current (Isc, microA/cm2) across muscle-stripped sheets of jejunum and ileum incubated in vitro after removal from fed rats, rats starved for three days, and chronically undernourished rats (50% of fed control intake for 21 days). Concentration and Isc response curves for serially-added mucosal Escherichia coli STa enterotoxin showed that the rats which had undergone dietary deprivation had a larger secretory Isc maximum but the ED50 values were unchanged compared with fed animals. In fed intestine the action of STa was transient, with an Isc peak and subsequent decay to the baseline over 60 minutes but in the undernourished intestine the response consisted of a significantly greater peak than that of the fed state (jejunum = 94%; ileum = 168%) and the Isc was maintained at or near the peak for at least 60 minutes. The starved intestine had a less well developed maintenance of its enhanced peak Isc. Serosal tetrodotoxin (1 microM) had no effect on the initial peak Isc values but caused a decay of the maintained Isc down to the basal or fed levels in the starved and, especially, in the undernourished intestines. Thus, dietary deprivation, especially chronic undernutrition, enhances the maximum electrogenic secretion due to STa and creates a new neural path in the submucosal plexus that, when activated by STa, maintains its enhanced secretory action. Its putative role in exacerbating secretory diarrhoea in malnourished human subjects could be an important component underlying the known relation between malnourishment and the increased severity of diarrhoea.

Oral rehydration solutions (ORS): enhancement by a soluble fiber

OBJECTIVE

This study was designed to test the hypothesis that, in an animal model of protein-energy malnutrition (PEM), carboxymethylcellulose (CMC), a viscous additive for the World Health Organization Oral Rehydration Solution (WHO-ORS), previously found to be effective in rats with osmotic diarrhea as an enhancer of water and sodium absorption, would also improve the performance of the WHO-ORS. This hypothesis was based on the changes in fluid and electrolyte transport that could be induced by an increase in the viscosity.

METHODS

We evaluated CMC in young rats fed a low-protein, low-energy diet for 3 weeks to induce PEM. Control (CTL) rats were fed a nutritionally complete diet. The ORS were tested with an in vivo perfusion procedure under anesthesia.

RESULTS

CMC addition (0, 2.5, 5.0 and 10.0 g/L) sharply increased the rates of net water and sodium absorption in both groups of rats, especially in the PEM animals. Net water absorption increased from (means +/- SEM) 0.75 +/- 0.06 to 2.21 +/- 0.18, 3.35 +/- 0.20 and 8.46 +/- 0.84 microL/min x cm in the PEM rats (0, 2.5, 5.0 and 10.0 g/L CMC, respectively). For the same CMC concentrations, sodium absorption improved from 178.8 +/- 20.3 to 402.4 +/- 18.4, 486.4 +/- 29.2 and 898.4 +/- 21.4 nmol/min x cm, respectively. CTL rats also showed marked increases. Rates of lumen-to-serosa water influx improved in both groups without major changes in water efflux. Net water and sodium absorption appeared related to the log of the ORS viscosity.

CONCLUSIONS

The results further support the concept that increased viscosity induced by CMC enhances the effectiveness of ORS.

Famine, fiber, fatty acids, and failed colonic absorption: does fiber fermentation ameliorate diarrhea?

The salvage function of the colon for absorption of unabsorbed sodium and water from the jejunum and ileum depends upon the metabolic integrity of colonic epithelial cells maintained by luminal short-chain fatty acids. With the depletion of luminal short-chain fatty acids under conditions of starvation, metabolic compensation from vascular substrates is incomplete. Loss of luminal short-chain fatty acids diminishes cell membrane integrity and causes secretion by colonic epithelial cells, leading to starvation diarrhea. Because sodium absorption is dependent upon CO2 production from n-butyrate, no compensatory absorption occurs during starvation. Under conditions in which luminal short-chain fatty acids are depleted, dietary fiber is useful as a low osmolality food constituent and for renewal of short-chain fatty acid levels by bacterial fermentation. The "antisecretory" effect of dietary fiber depends on the degree of the preexisting depletion of short-chain fatty acids and the methodology used to assess absorptive function. Dietary fiber has not been found harmful in refeeding starvation victims for whom it is an essential food constituent.

Lipid peroxidation and electrogenic ion transport in the jejunum of the vitamin E deficient rat

Increased concentrations of reactive oxygen species in children with depleted antioxidant defences have been implicated in a cycle of malnutrition, malabsorption, and infection leading to protracted diarrhoea. A rat model of chronic vitamin E deficiency has been used to study the effects of antioxidant depletion on jejunal structure and function in vitro. Basal intestinal short circuit current (Isc), a measure of net electrogenic ion movement across the intestinal epithelium, was greater in chronically vitamin E deficient jejuna than controls, as was the electrogenic secretory response to aminophylline and Escherichia coli STa but not to bethanechol. The galactose stimulated current was also greater in vitamin E deficient jejuna. Indices of lipid peroxidation (concentrations of thiobarbituric acid reactive substances and malondialdehyde) were increased in the vitamin E deficient small bowel. Small intestinal brush border membranes from vitamin E deficient animals displayed changes in both static and dynamic components of membrane fluidity measured by steady state fluorescence polarography. The results of these studies support the hypothesis that oxidative stress in subjects with compromised antioxidant defences results in small intestinal hypersecretion, which could predispose to or perpetuate protracted diarrhoea.

Intestinal hypersecretion of the refed starved rat: a model for alimentary diarrhoea

Fluid transport was gravimetrically measured in vivo in the duodenum, jejunum, and ileum of anaesthetised fed, 72 hour starved and 72 hour starved rats refed for up to five days after starvation. Basal unstimulated fluid transport was monitored by instilling 0.9% NaCl into the lumen and measuring the gain or loss in weight of the closed intestinal loop. Fluid was absorbed in all the areas of the intestine in the fed rats. Increasing basal fluid absorption was observed in the duodenum over the three days of starvation but in the jejunum there was no significant change. In the ileum, the pattern was very different, on day 1 the fluid was absorbed but on days 2 and 3 there was an increasing secretion of fluid. Refeeding the rats with their normal diet restored the basal absorption of fluid in the duodenum within 24 hours, had no effect in the jejunum but in the case of the ileum the hypersecretion of fluid observed in the day 3 starved rat was maintained on day 1 of refeeding, increased further on day 2, decreased on day 3 but returned to absorption on day 4. The normal absorption was restored to the ileum on day 5 of refeeding. Fluid secretion was induced in all the rat groups by bethanechol (ip 60 micrograms/kg bw) a stable cholinergic agonist, PGE2 (ip 10 micrograms/kg (bw) and E coli STa (luminally instilled, 500 ng/ml) a secretory enterotoxin. All the secretagogues gave enhanced secretion compared with the fed by day 2 of starvation which increased considerably on day 3. Refeeding returned their secretion back to the fed level in the duodenum within 24 hours, in the jejunum within 48 hours but in the ileum their induced secretion on day 2 of refeeding was greater than that of the day 2 of refeeding was greater than that of day 3 starved and took until day 4 to return to the fed levels for behanechol and PGE2 and until day 5 for E. coli STa. This behaviour of rat small intestine showing even greater hypersecretion in the refed state than the starved mimics the human condition of alimentary induced diarrhoea where incautious feeding of starved humans induces severe, often lethal diarrhoea. The refed starved rat appears to be a possible model for this condition.