Effects of the composition of solutions on water and solute absorption from the intact human intestine
In a series of systematic studies using a steady-state jejunal perfusion technique the influence of carbohydrate content and type, osmolality and sodium concentration on jejunal absorption was investigated. Carbohydrate content over the range from 225 to 440 mmol glucosyl units.1-1 did not increase intestinal carbohydrate or water absorption. The type of carbohydrate used also appears to have little effect on the rates of water or solute absorption from moderately hypotonic carbohydrate-electrolyte solutions. Solutions which were moderately hypotonic with respect to normal human serum promoted faster rates of water absorption than isotonic, which in turn were faster than that from hypertonic solutions. Increased rates of solute absorption were associated with faster rates of water uptake from the hypotonic solutions. Sodium chloride concentration over the range 22 to 44 mmol.1-1 did not affect water or carbohydrate absorption, although sodium chloride uptake tended to be faster from the solutions with the higher electrolyte content. Measurement of net and unidirectional water fluxes suggests that the increase in net water absorption in segmental perfusion studies is due mainly to a decrease in mucosa-to-lumen water flux. The pattern of water uptake, as assessed by deuterium accumulation in the circulation, generally appeared to follow the pattern indicated by the combined effect of the measured rate of gastric emptying and segmented water intestinal absorption. In conclusion, intestinal perfusion studies have identified moderate hypotonicity as the major factor in determining the rate of water absorption and an important influence in regulating solute transport from carbohydrate-electrolyte solutions. Although there was a tendency for hypertonicity to be associated with faster rates of deuterium accumulation in the circulation, this model of assessing water uptake indicated that the sodium content of the ingested drink was also an important factor.