The effect of certain dietary factors on the apparent absorption of magnesium by the rat

Abstract

Numerous workers have established a connexion between the metabolism of magnesium and various dietary factors. Thus Colby & Frye (1951 b) working with young rats on a low-Mg, low-calcium diet observed reduction in blood Mg levels and increase in mortality rate when the casein content of the diet was increased from 24 to 50 yo. , 1961). Thus, although it is evident that Ca and phosphate impair Mg absorption in certain animals, the relative and combined effects of these two factors have not been studied to any great extent.Mg absorption in healthy human subjects given a mixed diet low in protein and moderately low in Ca and supplemented with vegetables has been shown to be improved when protein replaced an equi-caloric amount of sugar or fat (McCance, Widdowson & Lehmann, 1942 (1955, 1957) have suggested that the high levels of ammonia that occur in the rumen of cows grazing spring grass may interfere with Mg absorption from the small intestine or may reflect a reduction in the concentration there of amino acids, which could also result in poorer absorption.In the experiments now reported the effect was studied of protein level, ammonium salts, Ca carbonate and sodium orthophosphate on the apparent absorption of Mg. The main object was to study factors affecting the absorption of Mg, and retention was determined in only one experiment. Rats were given diets containing about 20 mg Mg/Ioo g diet, a level reported adequate for growth and maintenance of normal levels of blood 1Mg in young rats (Kunkel & Pearson, 1948). Diets and general techniqueThe composition of, and content of some inorganic constituents in, the low-Mg basal diets and the experimental diets are given in Tables I and 2. Male hooded Norwegian rats were housed individually in metabolic cages of the Hopkins type (Ackroyd & Hopkins, 1916) and fed to appetite. Diets were moistened with distilled water to prevent scattering. I n addition, a vitamin mixture was given by pipette that provided a weekly dose of 1.4 mg DL-a-tocopherol, 360 i.u. vitamin A and 26 i.u. vitamin D. Distilled water was given in glass bulbs. Faeces and urines were collected daily and, at the end of the collection period, the separator, urine container and glass funnel were rinsed with hot, about o -~N -H C~, and the rinsings added to the urine. JOYCE TOOTHILL I963Ca was precipitated as the oxalate at pH 4-5 (Smith, 1957) and the tube and precipitate were washed once with about I ml distilled water; sodium citrate was used to prevent the co-precipitation of iron during the precipitation of the ammonium magnesium phosphate, and the 33 % (v/v) ammonia solution quoted by Godden (1937, p. 40) for washing the Mg precipitate was replaced by one of 10 yo (vfv) strength. Two precipitations of the Mg were found necessary for satisfactory results. The precipitate was finally dissolved in a small volume of about 2~-H h T 0~, the solution transferred to a volumetric flask and P determined as above. In order to check for manganese contamination, additional ammonium magnesium phosphate prec...

Increased Activity of Liver Xanthine Oxidase in Rats from Increasing Dietary Calcium

“…12 1 One unit was defined as that causing a change in absorbance of 1.0/min. The elements in tissues and diets were analyzed with a polarized Zeeman atomic absorption spectrophotometer (Model 180-80, Hitachi) as described previously 131 Dietary con- 15 1 Consistent with our previous report, 7 1 increasing dietary calcium caused an increase in the concentrations of liver molybdenum as shown in Table I. The activities of liver xanthine oxidase (0 type and D type) were also significantly increased by increasing calcium intake.…”

“…These rats were maintained on the test diet composed of 25% casein, 4% cellulose powder, 5% corn oil, and other nutrients as described previously. 7 1 Dietary calcium levels (0.05, 0.5, 1.5, and 2.5%) were adjusted by the addition of calcium carbonate. Composition of other elements in the salt mixture was the same as that reported by Ebihara et a/ 91 Deionized water and the diets were available ad libitum.…”

Effects of Varying Dietary Ratios of Magnesium, Calcium and Phosphorus in Growing Chicks

“…Several authors have shown nutritional interrelationships among calcium, phosphorus and magnesium in rats (Forbes, 1963;and Toothill, 1963), in dogs (Bunce et al, 1963) and in guinea pigs (Morris and O'Dell, 1963). Alder (1927) and Buckner et al (1932) reported better bone formation and egg production in laying hens when the magnesium content of the limestone added to the diet was low.…”

Effect of dietary calcium on secretion of calcitonin and gastrin in rats with medullary thyroid carcinoma

“…The serum magnesium concentrations showed changes reciprocal to the calcium intake and the calcium values in serum. A relationship between intestinal absorption of calcium and mag¬ nesium has been shown (Toothill 1963;O'Donnell & Smith 1973;Clark & Rivera-Cordero 1973) and a common transport system is probably involved (Alcock & Maclntyre 1962. The inverse relationship between the absorption of calcium and magnesium is also evident in man when a intake of one of the cations is reduced (Hanna et al 1960;Maclntyre et al 1961 iCT.…”