A computer model simulating the intestinal absorption of bile acids

Mathematical models were developed for assessment of the absorption kinetics of compounds passing down the length of a perfused intestinal segment. The models considered the intestinal segment as a cylinder composed of a large number of very small (infinitesimal) cylinders and described the concentration decline of the compound in situations with active, passive and combined active and passive transport. The maximal velocity of active transport, Vmax, the Michaëlis-Menten constant, Km, and the permeability coefficient, P, were calculated. A computer program was developed to operate the mathematical expressions. The models were validated by jejunal and ileal perfusions of various bile acids in six healthy volunteers. The fit between the mathematical models and the actually measured data showed an average standard deviation of 0.14 mmol/l (substrate infusion concentration ranging from 0.25 mmol/l to 3.0 mmol/l). It was concluded that the computer models were feasible for practical purposes. Moreover, the models reduced the number of perfusions necessary to determine the absorption kinetics of a given bile acid.