Probing intestinal permeability in man using different-sized, low-molecular-weight polyethyleneglycols and mathematical modelling

• Selective intestinal permeability as reflected by the urinary recovery of low-molecular-weight polyethylene glycols (PEG 400) of dlfferentsizes after oral administration was characterized with a mathematical filter-function. There was relative loss of both large and small PEG molecules on their way from the intestine to the urine. The reduced recovery of the large molecules is explained by selective intestinal absorption, since intravenous instillation abolished the effect. After curve-fitting to the experimental data, the mathematical procedure gives a quantitative measure of the fraction of selective and non-selective passage, and of filter-efficiency at different molecular weights. When applied to patients treated by bypass surgery for morbid obesity the method indicated a less permeable intestine with a reduced effective absorbtive surface area. In patients with rheumatoid arthritis a fasting diet gave a similar effect, which was accompanied by a reduction in disease activity. However, after changing to lactovegetarian diet the intestinal selectivity returned towards the control values, as did the inflammatory indices. Finally, to evaluate the importance of different physiological criteria for the outcome of the PEG 400 absorption test, a mathematical multi-compartment model was constructed and simulated on a computer.

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