A multicompartment model of vitamin B6 metabolism

The shape of the labelling curve for urinary pyridoxic acid following a single dose of labelled pyridoxine can be most easily described by a two compartment model. However, the usefulness of such a model is limited because the two pools have no physiological identity; the model does not describe the many metabolic interconversions associated with vitamin B6 metabolism; and the predictions of the total size of the vitamin B6 pool are not consistent with data from direct measurements. Therefore, we have been using the Simulation, Analysis, and Modelling program (SAAM) developed at the National Cancer Institute to develop an improved model. Since the SAAM 29 program is limited to 25 pools, only a few of the many tissue vitamin B6 pools could be included. Muscle and liver were chosen because they contain 80 to 90% of the vitamin B6 in the body. Plasma and erythrocytes were selected because of their importance in transport. This review traces the development of the model to its current stage and shows comparisons between the predictions of the model and a variety of data from the literature. At this point the emphasis has been on describing metabolism in rats because the most detailed kinetic data available were obtained from rats. The predictions of the current model do not match all available observations. However, the results are sufficiently encouraging to warrant continued development.