Gastrointestinal absorption of inorganic arsenic (V): The effect of concentration and interactions with phosphate and dichromate.

The absorption of inorganic pentavalent arsenic (As) by the rat small intestine was investigated using 2 different procedures: In vivo determination of overall extent of gastrointestinal absorption; and an intestinal perfusion technique. The aim was to determine the effect of concentration and the interaction with phosphate and dichromate anions on gastrointestinal absorption of As to understand the mechanism of As absorption at intestinal level. The results indicate there is a direct relationship, although not proportional, between the received dose and the absorbed amount of As. Intestinal absorption of As appears carried out by a saturable transport process. The phosphate produces a pronounced decrease in the intestinal absorption of As due to the fact that phosphate and As can share the same transport mechanism which is an active secondary carrier-mediated system depending on Na+ and H+ gradient. Addition of dichromate to perfusion buffers significantly (p > 0.05) increased As absorption. Several hypothesis may explain this fact: Dichromate produces pH modifications at the intracellular level, providing an adequate H(+)-gradient for As absorption; dichromate exerts a caustic effect, which damages the intestinal wall at the microvilli level. This allows free diffusion of As through the resulting openings.