Ruth Schwartz

Measurement of magnesium absorption in man using stable 26Mg as a tracer.

Abstract The stable isotope 26 Mg was compared to the radioisotope 28 Mg to estimate magnesium absorption in four healthy male subjects confined to a metabolic ward and consuming a constant diet for 146 days. Two isotopes tests were carried out in each subject on days 66 and 109 of the constant-diet period. In test 1, a solution containing 50 mg 26 Mg and 30 μC 28 Mg were taken orally during breakfast. In test 2, 50 mg 26 Mg were administered orally followed three hours later by an i.v. injection of 20 μC 28 Mg. True magnesium absorption was estimated by: (1) oral/i.v. ratios of 28 Mg in plasma and urine, or oral/i.v. 26 Mg/ 28 Mg ratios in urine; (2) the difference between intake and fecal excretion of total dietary magnesium over a period of 10 days, or of a single dose of either isotope, corrected for endogenous fecal magnesium. Estimates made in individual subjects by different procedures based on data derived solely by use of 28 Mg varied as much as estimates made by comparable procedures with data derived from either 26 Mg or 28 Mg. Measurements of 26 Mg enrichment in urine and feces were made by neutron activation analysis which loses precision at enrichment levels below 10% above natural abundance. With the doses used in this investigation only fecal samples collected within 3–4 days and urine samples taken wihin 2–24 h contained adequately detectable 26 Mg enrichment levels. Despite this limitation, 26 Mg significantly expands the scope of investigation of magnesium absorption in man beyond that possible with the short lived 28 Mg alone.

Mass spectrometry of a volatile Mg chelate in the measurement of stable 26Mg when used as a tracer.

A method for the detection of 26Mg enrichment of natural Mg was developed based on mass spectrometry (MS) of a Mg chelate made by complexing Mg to 2,2,6,6-tetramethylheptanedione (THD). The chelate [Mg(THD)2] was extracted at pH greater than 9 from dilute aqueous solutions into ethyl ether, recovered by sublimation at room temperature, and introduced by solid probe into a Finnigan 3300 mass spectrometer. The chelate was ionized by electron impact. Samples were heated to a maximum temperature of 200 degrees C at a rate of 700 degrees C/h. Each analysis required 1--5 micrograms Mg(THD)2. Enrichment levels as low as 5% above natural abundance could be detected satisfactorily. Precision was best at 26Mg enrichment levels of 8--40% above natural abundance, the levels most likely to be encountered in analysis of plasma, urine and fecal samples from experimental subjects who had received 26Mg as a tracer. The method was compared to neutron activation (NA) analysis and judged superior.

Aluminum accumulation in serum liver and spleen of fe-depleted and fe-adequate rats

AbstractThe study described here was planned to test the hypothesis that Al absorption and accumulation in the body are inversely related to Fe status. Aluminum3+ and Fe3+ have similar ionic radii and charge densities, pH-solubility relationships, and affinities for ligands, such as citrate and transferrin. Male weanling Sprague-Dawley rats were pair fed an Fe-deficient or Fe-adequate (control) diet for 2 wk. Each diet group was then randomly assigned to receive for four more weeks the Fe-deficient or adequate diet with:1.2% AlCl32.AlCl3+3.5% Na citrate; or3.No Al or citrate.n Iron depletion, confirmed by measurements of hemoglobin, hematocrit, serum Fe, and Fe binding capacity, increased concentrations of serum, liver, and spleen Al in all groups fed AlCl3. However, the increase owing to Fe deficiency was significant only when Al was fed with citrate. The data suggest that Fe deficiency enhances both Al absorption and accumulation in liver and spleen.

Effects of phytate reduction, fat extraction, and level of Ca on Ca and Zn bioavailability. Compared in vitro and in vivo.

The effect of phytate reduction, fat extraction, and addition of Ca in the form of skim or whole milk on Ca and Zn bioavailability from a breakfast containing bran muffins was studied in vitro and in vivo. Ca and Zn solubility were measured after in vitro simulated peptic and pancreatic digestion under pH conditions resembling those in the human GI tract. Absorption of Ca and Zn was measured in rats fed test meals tagged with45Ca and65Zn. Radioactivity in the femur and liver relative to levels found in rats injected with the isotopes served as criteria for45Ca and65Zn absorption, respectively.In vitro solubility was significantly depressed by the presence of phytate and inversely correlated with the phytate: Zn and the (phytate)(Ca): (Zn) ratios. Ca solubility was enhanced by extraction of fat and markedly increased by reduction in both fat and phytate. None of these effects was seen in vivo. However,65Zn absorption was significantly decreased by fat extraction and phytate reduction although this treatment increased in vitro Zn solubility. Possible reasons for these discrepancies are discussed.

The effect of magnesium deficiency on serum aldosterone in rats fed two levels of sodium

Abstract Rats were fed 47 (deficient) and 606 ppm (adequate) magnesium with either 2,100 or 14,000 ppm sodium. Serum corticosterone and aldosterone levels were determined by randoimmunoassay in six rats from each treatment group killed on days 7, 14, and 28 of consumption of the experimental diets. Serum corticosterone levels were moderately, but not significantly, decreased in magnesium deficient animals. Serum aldosterone levels increased over time in the rats fed the lower sodium diet with adequate magnesium and were further elevated in magnesium deficient animals. In sodium loaded rats the increase in aldosterone levels in magnesium deficiency was less and occurred later. Retention and urinary excretion of sodium and potassium did not appear to be affected by magnesium status or the serum concentration of aldosterone. Possible mechanisms underlying the changes in aldosterone levels of magnesium depleted animals are discussed with reference to the known effects of magnesium deficiency on physiological functions.

Stable 26Mgin as an In Vivo Tracer Investigation of Magnesium Utilization

A procedure using 26Mg as an in vivo tracer has been developed. Enrichment of biological samples containing 26Mg was measured by neutron activation following acid digestion and solvent extraction to remove the interfering nuclides 37Cl, 55Mn and other heavy metals. Special counting procedures minimized interference by 41Ar and 28A1 during neutron activation analysis. Interference of 24Na was minimized by mathematical channel by channel spectrum stripping. With current techniques, the lower limit of enrichment with 26Mg measurable with precision is 20% above the natural abundance of 11·24%. Good agreement was obtained of 26Mg and 28Mg retentions and estimates of the biological half-life when the two isotopes were administered simultaneously to rats either orally or by intraperitoneal injection.

Effect of Magnesium Deficiency on Intestinal Calcium Transport in Rats

Summary Calcium transport across the duodenum and ileum was measured by an in vivo ligated loop technique in Mg depleted rats and rats pair fed a magnesium adequate diet. Intestinal Ca transport and tibial 47Ca uptake were consistently decreased in magnesium depletion. Analysis of Ca fluxes, carried out by in situ perfusion, showed a significant decrease in passive diffusion, with less consistent effects on the saturable transport component. Both bone and plasma showed markedly decreased Mg concentration. Tibia Ca levels were slightly but significantly increased and plasma levels were either normal or slightly, but significantly elevated. The basis for the decrease in Ca transport of Mg depleted rats observed in this investigation is not clear. The data suggest a general alteration in mucosal membrane transport rather than a specific effect on Ca transport per se.

Cation excess of selected omnivore and vegetarian diets

Seven American‐type (US) and 3 Chinese‐type diets, selected to represent a range of food consumption patterns encompassing omnivore, lacto‐ovo‐vegetarian and vegan, were analyzed for Ca, Mg, Na, K, Cl, P and amino acid S. Dietary potential acid or base, as measured by cation excess total (cations ‐ anions), was calculated. Cation excess values ranged from ‐24 mEq in one of the Chinese diets to +70 mEq in the lacto‐ovo vegetarian diet. Regression analysis of cation excess vs. dietary protein sources showed a significant negative correlation with meat, and positive correlations with legumes and dairy products. No correlation was found between cation excess and sulfur or chloride values. Phosphorus, Ca, K, and to a lesser extent Mg, were all significantly positively correlated with cation excess. Contrary to expectations, total protein and amino acid‐S did not correlate with dietary acidity/alkalinity. Foods high in K, Ca, and Mg, such as vegetables, fruits, legumes, and dairy products were the most importan...