Dietary magnesium improves endothelial dependent relaxation of balloon injured arteries in rats
Introduction
Magnesium deficiency has been reported in diabetes, hypertension, and coronary heart disease [1]. Following therapeutic procedures such as coronary angioplasty, endothelial cell dysfunction is common and correlated with endothelial injury [2]. Experimental studies have shown endothelial denudation immediately after angioplasty and impaired endothelial reactivity for several weeks even in the presence of a regenerated endothelial surface 3, 4.
It is widely recognized that calcium plays an important role in the formation of endothelium-derived relaxing and constrictor factors 5, 6, 7, 8. Since magnesium has been described as a calcium antagonist agent capable of displacing calcium of intracellular sites and blocking the voltage-dependent L- or T-type Ca2+ channels and receptor-mediated Ca2+ permeable non-selective cation currents in vascular smooth muscle cells [9], it can affect the vascular reactivity to a number of vasoconstrictors and also the endothelial-dependent vasorelaxation for some agonists [10]. Therefore, the goal of the present study was to verify the importance of dietary magnesium on endothelium-dependent vascular relaxation during the healing process after balloon-injury.
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Animals
Male normotensive Wistar rats (Wistar EPM-1) weighing approximately 280±8 g were divided into six groups which received deionized water and a special diet containing 18% protein, 4% salt mixture, 1% vitamin mixture, 8% soybean oil 4% fiber and 65% corn starch. The salt mixture was modified to contain three concentrations of magnesium (g/kg chow); normal (1.0), high (2.0) and low (0.3). After three weeks, all animals were anesthetized by intraperitoneal injection of thionembutal (Abbott, 20
Serum magnesium and calcium levels
Serum calcium and magnesium levels determined 15 days after balloon injury were not affected by the high magnesium diet, but the animals fed a low magnesium diet presented the lowest magnesium serum levels, and also the highest ionized blood calcium levels (Table 1).
Histological analysis
Moderate intimal thickening of the thoracic aorta was observed on light microscopy only in the injured specimens. In the balloon-injured groups no significant differences in the ratio of intimal:medial area were observed among the
Discussion
Our results confirm that magnesium deficiency can be established rapidly through the diet [11]. However, magnesium supplementation in the diet did not lead to significant increase on its serum levels. Magnesium serum levels express only 1% of the total magnesium pool [12], a possible reason for this finding. Actually, in some studies, normal magnesium serum levels have been reported even in the presence of evident abnormality 13, 14. The inverse relationship between the magnesium content of the
Acknowledgements
The authors are grateful to Ms Ivete Ueda for assistance with laboratorial analysis, and CEDEME (Centro de Desenvolvimento de Modelos Experimentais para Medicina e Biologia) for providing the animals. This work was supported in part by CNPq (Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico) and a grant from Baldacci Corp.
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