Molecular radii of probes used in studies of intestinal permeability.

Molecular radii of probes used in studies of intestinal permeability SIR,-Many comments have been made about the usefulness of findings from studies of intestinal permeability in health and disease.The relationship of the observed urinary excretion of orally administered probes to molecular dimension, charge, and permeation pathway also has evoked much discussion.12 It has been suggested that, because of molecular size, smaller probes can cross the epithelial barrier via a transcellular pathway, whereas larger probes can only cross via an intercellular pathway.2L-rhamnose (MW 164 Da) and mannitol (MW 182 Da) belong to the former category and lactulose (MW 342 Da) and 5'Cr-