Effect of surfactants on the absorption of p-amino-benzoic acid from the rat intestine.

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Abstract
Effect of surfactants on the absorption of p-aminobenzoic acid (PABA) and p-acetamidobenzoic acid (Ac-PABA) from the rat intestine was investigated using the in situ recirculation technique. The surfactants tested were polyoxyethylene-(20)-sorbitol monooleate (Tween 80), polyoxyethylene-(9-10)-p-trans-octylphenol (Triton X-100), sodium dodecyl sulfate (SLS) and cetyltrimethylammonium bromide (CTAB). The micellar interaction of PABA and Ac-PABA with these surfactants was almost negligible except for CTAB. Ac-PABA absorption from the small intestine was increased by these 4 substances. The order of magnitude of the absorption enhancing effect was as follows: Triton X-100 > SLS .mchgt. CTAB .mchgt. Tween 80. PABA and Ac-PABA absorption from large intestine was also increased by 20 mM SLS. PABA exsorption to the small intestinal lumen was greatly increased by the addition of SLS to the perfusate. Despite such a general increase in the membrane permeability, PABA absorption from the small intestine was significantly inhibited by these 4 surfactants. The extent of inhibition was dependent on surfactant concentration and the exposure time of intestine to surfactants. SLS greatly accelerated protein release from the small intestine and an inverse correlation was found between the amount of released protein and PABA absorption in the presence of SLS. The specific inhibitory effect of surfactants may be attributed to the solubilization and the following release of protein, which is responsible for PABA absorption.