Magnesium absorption from distal part of swine digestive tract under isotonic and isoionic conditions from both sides of the epithelium

The effect of low magnesium concentrations in composed isotonic and isoionic Tyrode’s solution on its absorption from the distal part of the swine digestive tract was investigated in vitro on bags made of survived epithelia of the swine caecum and proximal colon. The epithelial side of either epithelium was always turned into the bags that were filled with Tyrode’s solution containing 0.5, 1.0 or 2.5 mmol/L magnesium. Tyrode’s solutions were always situated outside the bags, i.e., from submucosal side of the epithelium. At the beginning of the experiment and after 30, 60, 120 and 180 minutes of the experiment samples were taken from the solution outside the bags and analyzed spectrophotometrically for magnesium concentration. The excess of magnesium contents in the solution obtained in each experimental interval represents “the net flux” of magnesium in the direction of absorption. According to the results of the experiment, magnesium may be absorbed from both caecum and proximal colon epithelia against the concentration gradient, as well as under isotonic and isoionic conditions from both sides of the epithelium. The intensity of magnesium absorption depended on its concentration in the contents, on the epithelium used, and on the time of sampling. Results indicate the distal part of the swine digestive tract as the important part for magnesium absorption, especially under low concentrations in the contents. Under these experimental conditions the passive transport of magnesium played the major part.