Promotion of drug rectal absorption related to water absorption.

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Abstract
Promotion of the rectal absorption of antipyrine by sodium caprate (CA-Na) and diethyl maleate (DEM) was examined by in situ recirculating perfusion in the rat and compared with the results obtained previously with sodium ethylenediaminetetraacetate (EDTA-Na), a paracellular promoter. Both CA-Na and DEM significantly increased antipyrine absorption clearance (CLAP)and water inflex, in the same way as EDTA-Na. The increased levels of both CLAP and water influx caused by CA-Na were reduced to the control levels by ouabain, as was also found in the case of EDTA-Na. However, the promoting effect of DEM was decreased only slightly (not significantly) by ouabain treatment. These results indicate that the promotion mechanisms of CA-Na and DEM are different and that CA-Na works as a paracellular promoter in a manner similar to EDTA-Na.Antipyrine absorption through the paracellular route may possibly be promoted by water absorption dependent on active sodium transport.