INTESTINAL PERMEABILITY TO POLYETHYLENEGLYCOL AND SUGARS - A REEVALUATION

1. Previous studies have indicated that the permeability of polyethyle neglycol across the human intestine is anomalously high in comparison with the permeability of sugars with similar molecular mass. In conseq uence it has been proposed that two or more distinct mechanisms must e xist for the translocation of these classes of molecule or, alternativ ely, that the molecular parameter determining rate of penetration is e ach molecule's minimum molecular dimension. 2. The notional hydrogen-b onding capacity of a molecule correlates well with oil-water partition coefficient and also, in a variety of experimental systems, with rate of passive diffusion across biological membranes. A molecule's hydrog en-bonding capacity is calculated by inspecting the structural formula and summing the individual theory-derived hydrogen-bonding capacities of the molecule's functional groups. 3. A classic set of intestinal p ermeability data that includes several ethyleneglycol oligomers and se veral sugars is re-analysed. A good correlation between permeability a nd hydrogen-bonding capacity is demonstrated. Specifically, there is n o discontinuity between the polyethyleneglycols and the sugars. The da ta are compatible with a simple model in which all the molecules studi ed cross the intestine by passive diffusion across cellular membranes.