A novel assay of cell rubidium uptake using graphite furnace atomic absorption: application to rats on a magnesium-deficient diet.

The [Na,K]ATPase or sodium pump (SP) is a ubiquitous membrane cation transport system. Because of its potential participation in the pathophysiology of essential hypertension and cataract formation, the SP is under active investigation to detail its function and control. In this paper, we describe a novel, nonradioactive method of measuring SP ion transport activity in intact red blood cells (RBCs) using graphite furnace atomic absorption measurement of rubidium ion (Rb) uptake. This method provided sensitivity comparable to radioactive techniques, as assessed by experiments with human red blood cells (RBC) and ouabain, a known SP inhibitor, but this analytical approach eliminates the use of radioisotopes common to other Rb uptake assay methods. As a demonstration of its broader utility, the assay was used to assess the effects of dietary magnesium intake on SP-mediated ion transport in the RBCs of diet-controlled rats. Rats on 7 weeks of a magnesium-deficient (MgD) diet showed significant reductions in serum magnesium concentration, although levels remained in the lower region of the reference interval for healthy, magnesium replete animals. Red cell Rb uptake was significantly reduced in cells from the magnesium-restricted animals, demonstrating the sensitivity of Rb uptake to reduced magnesium intake, despite serum levels that fell within the reported normal range, and the utility of this Rb uptake assay in measuring physiological changes in SP function.

Geographical variations in heart deaths and diabetes: effect of climate and a possible relationship to magnesium.

BACKGROUND: Geographical variations in deaths from heart disease and the prevalence of diabetes occur in the United States. METHODS: These geographical variations, by state, were compared to the tertiles of the Z-score (Z-climate) obtained from the mean annual temperature and precipitation, by state, and to the tertiles of the Z-score (Z-environment) obtained from six environmental factors, by state, in monovariant analyses of variance. RESULTS: Both Z-scores were significantly related to male heart deaths (Z-climate: p = 0.000009; Z-environment: p = 0.000043) with Z-climate being the most significant. Both Z-scores were significantly related to the 1998 prevalence of diabetes (Z-climate: p = 0.00018; Z-environment: p = 0.0059) with the climate again being the most significant. CONCLUSIONS: Increased temperature can increase magnesium sweat losses, which may not be compensated by diet or water intake. Climate relationships to these diseases need further investigation.

A functional biological marker is needed for diagnosing magnesium deficiency.

Functional biological markers or biomarkers are now available for many nutrients which are used as nutritional status markers. Most sources of these biomarkers are products or precursors of enzymatic processes that can be measured in serum and plasma. At this time measurements of total or ionized magnesium (Mg) in serum, plasma, cellular components, urine or Mg retention from a load test are performed, but they may not always reflect Mg nutritional status. Biomarkers for Mg are needed which would reflect changes in biochemical processes where Mg is involved. Biomarkers for Mg need to be identified and evaluated in both animals and humans, with a determination of possible factors that may affect the reaction and biomarker concentrations. Some possible biomarkers for Mg include the following: Na/K ATPase, thromboxane B2, C-reactive protein, and endothelin-1. Other possible biomarkers for Mg need to be identified.

Magnesium deficiency during pregnancy in rats increases systolic blood pressure and plasma nitrite.

We investigated the effect of moderate dietary magnesium (Mg) deficiency, pregnancy, and concurrent L-arginine ingestion on systolic blood pressure (BP), nitric oxide production, serum Mg, and intrauterine growth restriction. Female rats, fed Mg deficient or sufficient diets from weaning, were divided into three groups: (1) nonpregnant, (2) pregnant, and (3) pregnant + 1% L-arginine in the drinking water. The systolic BP, plasma nitrite, serum Mg, and pup weights were determined. Data were analyzed using general linear model analysis of variance. In the pregnant rats, the Mg-deficient group had a significantly higher systolic BP (P =.0275) and plasma nitrite (P =.0244) compared to the Mg-sufficient group. L-Arginine ingestion significantly lowered systolic BP (P <.0001), and increased pup weight (P <.0067). Among the deficient groups, serum Mg was significantly lower (P =.0010) in pregnant rats without L-arginine, but was similar to the nonpregnant state in pregnant Mg-deficient after ingesting L-arginine. Moderate Mg deficiency, during the stress of pregnancy, adversely affected BP, nitric oxide production, and serum Mg. Supplemental L-arginine prevented these negative effects, possibly through a feedback loop by increasing nitric oxide syntheses, which increases cyclic guanosine monophosphate, which then increases free Mg and decreases free calcium. These ionic changes can act to decrease BP and modulate nitric oxide synthesis.