Interrelationships of chloride, bicarbonate, sodium, and hydrogen transport in the human ileum

Using a triple-lumen constant perfusion system, the following observations were made in normal subjects. First, chloride, bicarbonate, and sodium were found to exhibit net movement across ileal mucosa against electrochemical gradients. Second, during perfusion with a balanced electrolyte solution simulating plasma, the ileum generally absorbed, but sometimes secreted fluid. A reciprocal net movement of chloride and bicarbonate was noted when sodium movement was zero. Increasing rates of sodium absorption were associated with decreasing bicarbonate secretion rates and finally bicarbonate absorption. Even when bicarbonate was absorbed ileal contents were alkalinized (by contraction of luminal volume). Third, net chloride movement was found to be sensitive to bicarbonate concentration in ileal fluid. For instance, chloride was absorbed from solutions containing 14 or 44 mEq/liter of bicarbonate, but was secreted when ileal fluid contained 87 mEq/liter of bicarbonate. Fourth, when chloridefree (sulfate) solutions were infused, the ileum absorbed sodium bicarbonate and the ileal contents were acidified. Fifth, when plasma-like solutions were infused, the potential difference (PD) between skin and ileal lumen was near zero and did not change when chloride was replaced by sulfate in the perfusion solution. These results suggest that ileal electrolyte transport occurs via a simultaneous double exchange, Cl/HCO2 and Na/H. In this model neither the anion nor the cation exchange causes net ion movement; net movement results from the chemical reaction between hydrogen and bicarbonate. No other unitary model explains all of the following observations: (a) human ileal transport in vivo is essentially nonelectrogenic even though Na, Cl, and HCO3 are transported against electrochemical gradients, (b) the ileum can secrete as well as absorb, (c) ileal contents are alkalinized during absorption of or during secretion into a plasma-like solution, and (d) the ileum acidifies its contents when sulfate replaces chloride. Data obtained with a carbonic anhydrase inhibitor support the proposed model.

Mechanism of bicarbonate absorption and its relationship to sodium transport in the human jejunum

Using a constant perfusion technique, sodium and bicarbonate absorption was studied in human subjects. The following observations were made on sodium absorption from saline solution: (a) the rate of sodium absorption is markedly influenced by bulk water flow, (b) when net water flow is zero, sodium absorption is zero if there are no concentration gradients between plasma and lumen that favor net NaCl diffusion; and (c) the PD between abraded skin and jejunal lumen is near zero when saline is perfused and does not change with partial substitution of sulfate or bicarbonate for chloride. Based on these observations, we conclude that sodium absorption from saline is entirely passive in the human jejunum. On the other hand, in the presence of bicarbonate sodium is absorbed actively against electrochemical gradients. The mechanism of the link between bicarbonate and sodium absorption was studied in normal subjects and in 11 patients with pernicious anemia; the latter were chosen because they do not secrete gastric acid which can react with bicarbonate in the jejunal lumen. We observed that bicarbonate absorption (a) occurs against steep electrochemical gradients, (b) does not generate a potential difference between abraded skin and jejunal lumen, (c) is inhibited by acetazolamide, and (d) generates a high CO2 tension in jejunal fluid. These observations suggest that bicarbonate absorption is mediated by active hydrogen secretion, rather than by bicarbonate ion transport per se, and that the link between sodium and bicarbonate transport is best explained by a sodium-hydrogen exchange process.

Stimulation of active and passive sodium absorption by sugars in the human jejunum

The effects of glucose and fructose on water and sodium absorption in the human jejunum were compared to assess the relative contribution of active and passive sugar stimulation of sodium transport. The effect of fructose is assumed to be entirely passive, and the difference between the effects of fructose and glucose is assumed to be a measure of sugar-stimulated, active sodium absorption. Water and sodium movement with mannitol was the base line. Three sets of test solutions with differing sugar concentrations were studied. Fructose stimulated 66-100 per cent as much net sodium and water absorption as glucose. Fructose stimulated potassium absorption, whereas glucose stimulated potassium secretion. Urea absorption was stimulated by both sugars. Glucose and fructose stimulated sodium absorption when chloride was the major anion, but they had relatively little effect on net sodium movement when chloride was replaced by bicarbonate or sulfate. It is concluded that glucose stimulates passive and active sodium transport in the human jejunum. Stimulated active sodium absorption generates an electrical potential across the mucosa that causes sodium (and potassium) secretion and partly or completely nullifies the effect of active sodium transport on net sodium movement. Net sodium absorption sitmulated by glucose is mainly (66-100 per cent) the passive consequence of solvent flow. The accompanying anion determines the degree to which sugars stimulate sodium absorption (C1 greater than SO-4 greater than HCO3). The effects of bicarbonate and sugars on jejunal sodium absorption are not additive.

Potassium transport in the human small bowel

Perfusion experiments in the small intestine of normal subjects and in the ileum of patients with ileostomies demonstrated that the distribution of potassium across the mucosa was compatible with a passive process for transport. In the jejunum potassium transport was shown to be markedly influenced by solvent drag and the jejunal mucosa appears to be more permeable to potassium than to sodium. This permeability was apparently unaffected by calcium in the lumen in concentrations of between 1·15 and 7·25 m-equiv/1. In the ileum potassium transport was influenced by changes in luminal sodium concentration and it is suggested that this is a passive consequence of the change in electrical potential which the change in sodium concentration induces. The electrical potential is thought to be a sodium diffusion potential. All the evidence thus points to a purely passive behaviour of the small intestine towards potassium.

Oral therapy in children with cholera: a comparison of sucrose and glucose electrolyte solutions

We performed a double-blind trial comparing sucrose electrolyte oral solution with glucose electrolyte oral solution in children less than 5 years of age with severe cholera-like diarrhea. Of 111 patients studied (102 with bacteriologically confirmed cholera), 55 received sucrose solution and 56 received glucose solution. The success rates, as defined by the absence of the need to give unscheduled intravenous therapy, were similar in the two groups (73% and 77% in the sucrose and glucose groups, respectively). There was no difference in purging rates between the two groups. The primary determinant of success for oral fluid regardless of the sugar was the purging rate. Sucrose malabsorption was responsible for oral therapy failure in one child. This study demonstrates that sucrose is an effective alternative to glucose in the oral therapy solution, but either must be used in conjunction with intravenous solution when treating severe dehydrating diarrhea.

Efficacy of mung bean (lentil) and pop rice based rehydration solutions in comparison with the standard glucose electrolyte solution

Children with acute diarrhea and moderate dehydration between 3 months and 5 years of age were randomly assigned to receive treatment with standard WHO oral rehydration solution (ORS) (n = 33) and two other solutions in which the 20 g/L glucose was substituted by 50 g/L of pop rice (n = 31) and 60 g/L of mung bean (lentil) powder (n = 29). Satisfactory oral rehydration, as assessed clinically and by changes in PCV and total serum solids (TSS), was achieved in 90.9% with WHO ORS, 96.8% with pop rice, and 96.6% in the mung bean ORS treated group (p greater than 0.05). The purging rates (ml/kg/h) until recovery were 2.49 +/- 1.5 (pop rice); 2.91 +/- 2.0 (WHO), and 3.41 +/- 1.7 in the mung bean group (p greater than 0.05). The percentage of patients recovering from diarrhea within the 72 h study period was 58.0 (pop rice), 48.4 (WHO), and 44.8 for mung bean group (p greater than 0.05). Though differences in stool volumes and duration in the three groups were not statistically different, there was a trend toward improvement in efficacy with the pop rice ORS in several parameters: greater weight gain, higher percentage decline in TSS, higher urine output despite lower ORS intake, and lower purging rates. The intake of semisolids in the 24-72 h study period was also higher in the pop rice group as compared to the other two groups (p less than 0.05). The number of breast feeds and intake of artificial milk was however similar in all groups (p greater than 0.05).

Glycine-based oral rehydration solution: reassessment of safety and efficacy

We evaluated the safety and efficacy of a glycine-based orally administered rehydration solution by comparing it with a standard oral rehydration solution (ORS) without glycine in a randomized double-blind trial in United States infants (age less than 15 months) given treatment for acute gastroenteritis as inpatients or outpatients. The response to therapy (stool volume and duration of illness) was similar in the two groups, except that in four (13%) of 31 hospitalized infants receiving glycine-ORS hypernatremia developed, (one had symptoms) compared with none of 35 receiving ORS (P less than 0.04). Among the 77 outpatients there were no differences between the groups. This study demonstrates that glycine-ORS did not provide any therapeutic advantage over standard ORS, and hypernatremia developed in some patients receiving glycine-ORS. We suggest that caution be used with this type of solution until further safety studies have been done.

Sucrose in oral therapy for cholera and related diarrhoeas

Sucrose was tested as a possible alternative to glucose in oral diarrhoea therapy. Eighteen patients were given oral sucrose plus electrolytes as a maintenance solution. Fifteen of these patients could be maintained using this solution, but three developed massive increases in net fluid losses with increases in plasma specific gravity, necessitating termination of oral therapy. Twelve patients tested all had significant concentrations of stool reducing sugar. The data contrast with the rarity of treatment failures of oral glucose-electrolyte solutions. Glucose, therefore, is preferable to sucrose for oral therapy of diarrhoeal diseases.

Home-administered oral therapy for diarrhoea: a laboratory study of safety and efficacy

Serum electrolytes were measured for persons treated for diarrhoea at home with prepackaged or locally available sugar and salt oral rehydration therapy (ORT) solutions and for persons with diarrhoea who received no ORT but were treated according to local customs. No detrimental effect was found for persons treated with ORT at home; no significant difference was found in the frequency at which members of the groups had hypernatraemia. The rates of hyponatraemia and hypokalaemia were significantly lower for persons who took estimated appropriate volumes of ORT than for those who took less than appropriate volumes or for persons treated according to local customs without ORT. These laboratory results indicate that ORT administered in rural homes in Bangladesh was safe and effective under the conditions of our study.

Comparison of glucose/electrolyte and glucose/glycine/electrolyte oral rehydration solutions in hospitalized children with diarrhea in Costa Rica

The experience of Nalin et al. and Patra et al. with a "super oral rehydration solution (ORS)" containing glucose plus glycine to enhance the intestinal absorption of sodium and water prompted us to investigate a similar ORS containing the standard World Health Organization (WHO/ORS) plus either 55 or 110 mmol/L glycine in infants and small children with noncholera diarrhea. We did not find a statistically significant difference between the glycine-fortified ORS and the standard WHO/ORS with respect to the clinical outcome and composition of serum electrolytes.