Differences in the promotion mechanism of the colonic absorption of antipyrine, phenol red and cefmetazole.

The promotion of antipyrine, phenol red and cefmetazole absorption by sodium ethylenediaminetetraacetate (EDTA-Na) as a paracellular promoter, diethyl maleate (DEM) as a transcellular promoter, and sodium taurocholate (TC-Na), whose promotion mechanism is still unclear, has been investigated by the rat in-situ colonic loop technique. All these promoters increased AP absorption and water influx from the lumen to the blood. Ouabain treatment suppressed the increase in antipyrine absorption and water influx induced by TC-Na and EDTA-Na, but did not modify the enhancing effect of DEM. Thus, the promotion mechanism of TC-Na may be similar to that of EDTA-Na. Phenol red and cefmetazole absorption were increased by TC-Na and EDTA-Na but not by DEM. Accordingly, phenol red and cefmetazole absorption appears to be promoted via paracellular but not transcellular routes. The collection of blood for plasma samples reduced the influx of water which had been increased by TC-Na or EDTA-Na. Consequently, the enhancement in antipyrine plasma concentration by these promoters was reduced to the control level. The inhibitory mechanism for this is discussed on the basis of the blood-flow limitation of antipyrine and water absorption.