Net Absorption Of Magnesium Research Articles

Effect of calcium on magnesium absorption.

The effect of calcium on magnesium absorption was studied in the rat ileum in vivo. The increase in the luminal concentration of calcium led to a progressive decrease in magnesium absorption, which was accompanied by a parallel decrease in net sodium absorption. This calcium effect was also observed when sodium chloride was replaced by urea. However, a consistent correlation was observed between the magnitude of net magnesium absorption and the rates of net water absorption of all calcium concentrations. These findings suggest that calcium decreases magnesium absorption by a nonspecific reduction in membrane permeability to solutes that induce net water flow and are consistent with the concept that magnesium is transported by solvent "drag". The increase in the luminal concentration of calcium resulted in an increase in tissue accumulation of magnesium. This increase in tissue accumulation of magnesium was associated with a decrease in net sodium absorption and in the negativity of the transmural PD. These findings suggest an additional mechanism of magnesium transport operating independently of net water flow.

Studies on the amount and composition of digesta flowing through the duodenum of dairy cows. 2. Sites of net absorption of magnesium and calcium from the alimentary tract.

Two cows were fitted with re-entrant duodenal cannulas, and four with T-piece duodenal annulas. Balance trials were carried out, the cows receiving either a winter ration, or freshly-mown herbage. Direct measurements were made of the flow of digesta, and of the amounts of Mg and Ca in both duodenal and faecal samples. Also indirect measurements were made of these parameters, using polyethylene glycol and chromium sesquioxide indicators. Net Ca absorption was restricted to the intestines, and, at high Mg intake, net Mg absorption was also largely intestinal, though too large an error attached to the indirect measurement of Mg absorption rates for reliable conclusions to be drawn. There was considerable secretion of Ca proximal to the duodenum. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Influence of feeding regimen and protein supplementation on the sites of net absorption of magnesium in sheep.

1. Sheep prepared with a rumen cannula and with re-entrant cannulas at the proximal duodenum and terminal ileum were given diets of dried grass, and dried grass supplemented with formalin-treated or untreated casein. They were fed either continuously or once daily. Paper impregnated with chromic oxide was given once daily via the rumen fistula.2. The observed daily flows of magnesium at the duodenum and ileum were highly correlated with the corresponding flows of Cr.3. There was a net absorption of Mg from the stomach as well as the intestinal region of all sheep.4. Protein supplementation had no effect on the extent or sites of Mg absorption, but altering the feeding regimen changed the proportions of the net absorption of Mg occurring in the stomach and intestinal regions.

Magnesium Metabolism in Primary Hyperparathyroidism

1. Magnesium metabolism has been studied in forty-eight patients with primary hyperparathyroidism. Metabolic balance studies were undertaken in forty-three untreated patients and in fifteen patients after parathyroidectomy. The data obtained are compared with the pattern of magnesium metabolism in healthy adults, as established by analysis of collected nutritional studies. The renal handling of magnesium was assessed from measurements of 24-h renal clearances. 2. The mean serum magnesium in primary hyperparathyroidism was normal but low levels were present in nine of the forty-eight patients. There was a significant inverse correlation between serum levels of calcium and magnesium. 3. The magnesium balance was negative by amounts >5% of the dietary intake in eleven patients, and positive to a similar degree in twenty-one. Patients in negative balance ingested and consequently absorbed less magnesium than those in positive balance; the negative balance was apparently due to inadequate renal conservation of magnesium in the face of this lower intake and, in some cases, despite a low serum magnesium. When related to the level of dietary intake, intestinal net absorption of magnesium tended to be greater than normal. 4. In eleven of twelve patients studied, the urinary output of magnesium was lower after parathyroidectomy irrespective of changes in the serum level of magnesium. This fall in output appeared to depend mainly on reduction in the serum calcium. In untreated patients without advanced secondary renal disease there was a positive correlation between the serum calcium and the clearance ratio CMg/Ccreatinine. Additional mechanisms may contribute to renal loss of magnesium when renal failure is advanced. 5. The tendency to develop a negative magnesium balance and hypomagnesaemia in untreated patients of this series thus appeared related to the height of the serum calcium, the presence of advanced secondary renal disease and inadequate dietary intake. 6. Significant and sustained hypomagnesaemia after parathyroidectomy occurred only in patients with generalized bone disease. Its development appeared to depend on the inadequacy of the ordinary diet to meet the combined requirements for magnesium of new soft tissue formation and deposition in mineralizing bone.

Effects of magnesium on calcium and phosphate metabolism in parathyroidectomized rats.

Raising dietary magnesium from low to high level increased calcium absorption and urinary calcium in parathyroidectomized rats. The net result was increased calcium balance and serum calcium levels in parathyroidectomized rats to approximately normal levels. Supplemental magnesium decreased urinary phosphate in parathyroidectomized rats and phosphate balance and serum phosphate levels were restored to almost control values. Lowering dietary magnesium had the opposite effect on calcium and phosphate absorption and excretion. Although magnesium ions have been reported to have effects on parathyroid function, the results observed in these studies indicate that magnesium ions have a singular effect on calcium and phosphate metabolism irrespective of the presence or absence of the parathyroid gland. Parathyroidectomy had no significant effect on net magnesium absorption. (Endocrinology 85: 1103, 1969)

Net movements of magnesium and calcium in the rat small intestine in vivo.

SummaryMagnesium absorption by the rat small intestine in vivo was studied by a perfusion technique under controlled conditions. Net magnesium absorption per unit weight of intestinal segment was significantly greater in duodenum than in ileum. However, comparisons with previous studies of calcium transport using a similar experimental model show that magnesium was less well absorbed than calcium in the duodenum, while ileal absorption rates were almost equal. Tissue concentrations of magnesium were higher in the duodenum than in ileum, the reverse of the pattern for calcium. Neither tissue calcium nor the secretion of calcium into the intestinal lumen was influenced by transported magnesium.We thank Dr. Paul E. Leaverton for his advice and help with statistical analyses of the data.

Effect of the ingestion of wood shavings on magnesium and calcium utilization by milk-fed calves

1. The amounts of wood shavings eaten by a group of unmuzzled calves allowed unlimited access to the shavings but fed otherwise only on milk were estimated by a lignin ratio technique. The amounts increased to a mean value of about 250 g. dry weight/day at 13–14 weeks of age.2. Although a marked decrease in net magnesium absorption from the diet occurred with age in a group of efficiently muzzled milk-fed calves the mean decrease was not as great as that in the group of unmuzzled calves when the latter were eating considerable amounts of wood shavings. Data are presented which show that the difference is accountable by the excretion in the faeces of some of the magnesium in the increased flow of endogenous fluid from the rumen (probably mainly saliva) in the unmuzzled calves. The results suggest that many milk-fed calves (assuming about 11–12 mg./100 ml. magnesium in the milk) will resist hypomagnesaemia for at least 5 months but only if they are effectively prevented from chewing foreign matter. This may partly account for previously observed variations in. the ages at which calves develop hypomagnesaemia.3. Net calcium absorption from the diet decreased with age in both the muzzled and unmuzzled groups of calves but again to a greater extent in the unmuzzled group. The difference was much greater than could be accounted for by increased loss of endogenous calcium due to greater saliva production in the unmuzzled calves. It appeared that the shavings contained a factor (not phytate) which interfered with calcium utilization. It is suggested that the factor might act by inhibiting the action of vitamin D.