Intestinal calcium absorption in the rat after oral Tween 80 administration

Calcium absorption into rat intestine was investigated in vitro and in vivo after oral administration of Tween 80 (Polyoxyethylene (20) sorbitan monooleate). The in vivo study showed a significant decrease in serum calcium and in the quantity of calcium excreted by the intestine. In vitro, measurement of calcium influx into slices of intestine taken from Tween 80 treated animals showed that passive calcium diffusion was unchanged and that a decrease in the active transport alone is responsible for reduction in total calcium influx. Lineweaver-Burk analysis of the saturable component of calcium flux showed that the main variation was not due to a change of affinity of the system for the calcium but a decrease of the maximal calcium influx. Thus there are some arguments in favor of non-specific modifications of intestinal medium affecting calcium bioavailability rather than a specific action on the carrier.