Magnesium absorption from different compartments of the swine large intestine

We studied magnesium absorption in the distal part of the swine intestine a s a function of different magnesium concentrations in the contents that may affect its absorption rate. The study was carried out in vitro by using sa cs made of surviving mucous membrane of the caecum and proximal colon. The sacs were filled with magnesium chloride solutions containing magnesium at 0.5, 1.0, 2.5, 5, 10 or 20 mmol/L. The samples were collected on the submuc osal side of the mucous membrane at the beginning of the experiment and 30, 60, 120 and 180 minutes later. Magnesium concentration in the samples was determined spectrophotometrically using the Titan yellow method. increase o f its concentration on the submucosal side was noticed already after 30 min utes from both compartments at all magnesium concentrations in the contents (P < 0.001). According to the presented results, at the lowest magnesium c oncentration in the contents, its absorption against the concentration grad ient is possible from both compartments. The increase of magnesium concentr ation in the contents to 10 or 20 mmol/L was accompanied by a significant i ncrease of its absorption from both compartments (P < 0.001). The lowest ab sorption rate of magnesium was achieved at 5 mmol/L of magnesium in the con tents. The epithelium of the caecum was less resistant to low and proximal colon to high magnesium concentration in the content. Our results indicate that the distal part of the swine digestive tract, i.e. the caecum and prox imal colon, represent important sites of the magnesium absorption where mag nesium was mostly absorbed by passive transport.