Effects of magnesium deficiency on duodenal and ileal magnesium absorption and secretion

Intestinal adaptation by the growing rat to a low-magnesium diet was studied by in situ perfusion of duodenum and ileum in vivo. Rats were fed diets containing either 0.066 or 0.022% Mg for 3 weeks. Magnesium-restricted rats became hypomagnesemic and hypercalcemic. Net magnesium secretion was studied by perfusing an initially magnesium-free saline solution; secretion was higher in duodenum than in ileum, and decreased significantly in the duodenum in response to magnesium restriction. Net magnesium adsorption studied by intraluminal perfusion of 2.5 mM magnesium in saline was greater in duodenum than ileum in rats taking a low-magnesium diet, but duodenal and ileal absorption did not differ in animals taking the normal magnesium diet. Absorption did not adapt significantly to magnesium restriction in either segment. Adaptation of small-intestinal magnesium transport to a low magnesium diet is minimal, consisting mainly of reduced duodenal magnesium secretion.     

Vitamin D dependence and aboral gradient ofin vivo intestinal calcium transport in the rat

Rates of small-and large-intestinal calcium transport and their dependence on low doses of vitamin D were compared. Young rats were depleted of vitamin D by feeding a rachitogenic diet for 8–9 weeks; 48 and 24 hr prior to study, half were repleted with 200 IU vitamin D₂. Duodenum and ileum, or cecum and colon, were perfused separately in situ with 1.6 mM calcium and tracer⁴⁵Ca in saline. There was an aboral gradient for net calcium transport and lumen-to-plasma flux with higher values in proximal than distal segments. Vitamin D repletion increased net calcium flux and lumen-to-plasma flux in duodenum and ileum, but not cecum and colon. Plasma-to-lumen flux (calculated as the difference between lumen-to-plasma flux and net flux) tended to be higher in colon than other segments and was not altered by vitamin D repletion.     

Effects of magnesium deficiency on duodenal and ileal magnesium absorption and secretion

Intestinal adaptation by the growing rat to a low-magnesium diet was studied byin situ perfusion of duodenum and ileumin vivo. Rats were fed diets containing either 0.066 or 0.002% Mg for 3 weeks. Magnesium-restricted rats became hypomagnesemic and hypercalcemic. Net magnesium secretion was studied by perfusing an initially magnesium-free saline solution; secretion was higher in duodenum than in ileum, and decreased significantly in the duodenum in response to magnesium restriction. Net magnesium absorption studied by intraluminal perfusion of 2.5 mM magnesium in saline was greater in duodenum than ileum in rats taking a low-magnesium diet, but duodenal and ileal absorption did not differ in animals taking the normal magnesium diet. Absorption did not adapt significantly to magnesium restriction in either segment. Adaptation of small-intestinal magnesium transport to a low magnesium diet is minimal, consisting mainly of reduced duodenal magnesium secretion.This study was supported in part by Research Grant AM02534 and Training Grant AM5390 from the National Institutes of Health.