Site and mechanism of intestinal magnesium absorption.

Despite considerable research on magnesium (Mg) absorption there is still uncertainty regarding the site and mechanism of intestinal Mg transport. A careful review of the literature indicates that while Mg is absorbed throughout the intestine, the predominate site is the distal small intestine. There are three mechanisms by which Mg has been shown to cross the intestine:passive diffusion, solvent drag, and active transport. The importance of each of these mechanisms to total Mg absorption is discussed. Studies in both humans and experimental animals indicate that passive diffusion through the paracellular pathway accounts for the majority of Mg absorbed. Investigators have also consistently demonstrated the existence of a saturable component. Studies in everted gut sacs, however, have failed to demonstrate that Mg is actively transported against a concentration gradient in young or adolescent rats. Recent studies using the Ussing chamber have documented that Mg is actively transported in the descending colon.