Fluorescence study of the membrane-perturbing action of sodium caprylate as related to promotion of drug absorption.

The medium-chain fatty acid sodium caprylate released 6-carboxyfluorescein (CF), a model compound of water-soluble drugs, from the rat small intestinal brush border membrane (BBM) vesicles and liposomes containing CF. Caprylate caused a decrease in the fluorescence polarization of dansyl chloride, fluorescein isothiocyanate, and eosin maleimide covalently labeled to BBM. This indicates a perturbation of the BBM. However, no change in the fluorescence polarization of lipid-soluble fluorescent probes (2-(9-anthroyloxy) stearic acid, 12-(9-anthroyloxy) stearic acid, and 1,6-diphenyl-1,3,5-hexatriene) labeled to BBM was produced by caprylate. These findings indicate that caprylate can increase the permeability of the plasma membranes through the perturbation of the membranes. These actions of caprylate on membranes are considered one possible mechanism by which it promotes the absorption of water-soluble and poorly absorbed drugs.