Age-dependent alterations of intestinal absorption. I. Theoretical aspects.

To test the absorption of orally administered D-xylose in the upper small intestine its concentration in the blood plasma must be measured. Absorption is determined as a function of time by subtraction of the blood values found after intravenous administration, which would indicate the rates of metabolism and extraction of xylose by the body. It is suggested that comparison with the behavior of a proposed four compartment model may give a biological interpretation of the results. The possible dependence of amount and rate of absorption can be determined if the same time after feeding of the same diet is used in each absorption measurement. It is suggested that the time point to be used for administration be that time at which the highest concentration of xylose in the peripheral blood is found.