Human intestinal water absorption: direct vs. indirect measurements

Abstract

Distilled water, a carbohydrate-electrolyte (CE; 4% sucrose, 2% glucose, 17.2 meq/l NaCl, and 2.8 meq/l KCl) solution, or a 10% glucose solution, all containing the nonabsorbed indicator polyethylene glycol (PEG) and deuterium oxide (D2O, 30 ppm), were infused (15 ml/min) into the duodenojejunum of seven men by using the triple lumen technique. Net water absorption was determined directly from the change in PEG concentration and was calculated from plasma D2O derived from D2O in the perfusion solutions. The protocol included a 45-min equilibration period followed by a 90-min test period. Intestinal samples were drawn at 10-min intervals from 15 to 45 min and at 15-min intervals thereafter. Blood was drawn at 45, 50, 55, 60, 75, 90, 105, 120, and 135 min. Intestinal samples were analyzed for D2O, Na+, K+, osmolality, PEG, and glucose; blood was analyzed for D2O. Results (+/- SE; positive values secretion, negative values absorption) showed net fluid absorption from distilled water (-9.40 +/- 1.28 ml.h-1.cm-1) and the CE (-13.30 +/- 1.22 ml.h-1.cm-1) solution, but net secretion (4.40 +/- 1.25 ml.h-1.cm-1) from the 10% glucose solution. All values were significantly (P less than 0.05) different from each other. Perfusing the CE solution caused net Na+ and K+ absorption, whereas perfusing the 10% dextrose solution caused net electrolyte secretion. Rates of D2O accumulation in the plasma were independent of the solutions perfused.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of a deuterium tracer technique to follow the fate of fluids ingested by human subjects: effects of drink volume and tracer concentration and content

“…In contrast to the results of Gisolfi et al (1990) andRehrer et al (1992), there are data to show that there is good agreement between the results of perfusion studies and those obtained with the deuterium tracer method. Leiper et al (1988a) have reported that the rate of deuterium accumulation was about 50% faster after ingestion of a dilute carbohydrateelectrolyte solution than after ingestion of plain water: this same solution was shown to slightly slow the rate of gastric emptying (Leiper et al 1988b) but to promote an increase in the rate of intestinal water uptake (Leiper & Maughan, 1986).…”

“…In spite of the evidence to show that the tracer accumulation method produces results that are in broad agreement with predictions made on the basis of the known gastric emptying and intestinal water absorption characteristics of the test drinks compared, doubts have been raised as to the usefulness of this technique (Gisolfi et al 1990). In the study of Gisolfi et al (1990), the net rate of water flux in a segment of the small intestine was measured using a triple lumen perfusion method while three different solutions were perfused at a fixed rate; the test solutions were distilled water, a 6% carbohydrate-electrolyte solution and a 10% glucose solution.…”

“…In the study of Gisolfi et al (1990), the net rate of water flux in a segment of the small intestine was measured using a triple lumen perfusion method while three different solutions were perfused at a fixed rate; the test solutions were distilled water, a 6% carbohydrate-electrolyte solution and a 10% glucose solution. Deuterium was added as a tracer to all the test solutions.…”

“…The use of a continuous infusion into a short segment of the small intestine of a test solution with a constant tracer concentration does not reflect the situation that exists after ingestion of a single bolus of a test drink of the same composition. Solute and water fluxes will vary greatly along the length of the small intestine, and the short (40 cm in the study of Gisolfi et al 1990) segment through which the test solution is perfused may not be representative of the situation that exists when the whole length of the gut is available for exchange (Rolston et al 1990). After ingestion of a single bolus of a labelled solution, the concentration gradient from lumen to mucosa will decrease as the tracer is absorbed.…”

“…Objections have been raised to the use of the tracer method as employed in the studies referred to above, as water movement in the intestine is a bi-directional process, and tracer will accumulate in the blood even when net secretion of water is occurring in the small intestine (Gisolfi et al 1990). Nonetheless, the results of Davis et al (1987) who compared solutions of different composition were largely those that would have been expected from the known gastric emptying and intestinal absorption characteristics of the solutions being compared.…”