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-t-octylphenol (Triton X-100), sodium dodecylsulfate (SLS) and cetyltrimethylammonium bromide (CTAB). The micellar interaction of PABA and Ac-PABA with these surfactants were almost negligible except CTAB. The absorption of Ac-PABA from the small intestine was increased by these four surfactants. The order of magnitude of the absorption enhancing effect was as follows : Triton X-100>SLS≤CTAB>>Tween 80. The absorption of PABA and Ac-PABA from the large intestine was also increased by 20 mM SLS. In addition, the exsorption of PABA to the small intestinal lumen was greatly increased by the addition of SLS to the perfusate. In spite of such a general increase in the membrane permeability, the absorption of PABA from the small intestine was significantly inhibited by these four surfactants. The extent of inhibition was dependent on the concentration of surfactants and the exposure time of intestine to surfactants. SLS greatly accelerated the release of protein from the small intestine and an inverse correlation was found between the amount of released protein and the absorption of PABA 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 the absorption of PABA.
