Magnesium depletion impairs myocardial carbohydrate and lipid metabolism and cardiac bioenergetics and raises myocardial calcium content in-vivo: relationship to etiology of cardiac diseases.

Abstract

This study examines the effects of Mg depletion on myocardial bioenergetic, carbohydrate, lipid and phospholipid metabolism. Rats were studied after long-term (12 week) selective dietary restriction of Mg (20% normal dietary intake). Myocardial biopsy samples were examined for glucose 6-phosphate and glycogen to evaluate carbohydrate pathways and for glycerol phosphate and mitochondrial fatty acid oxidation and phospholipid contents to evaluate lipid and phospholipid turnover. Dietary Mg deficiency resulted in falls in myocardial glycogen, glucose-6-phosphate, glycerol phosphate, as well as the contents of phosphatidylcholine (PC), phosphatidylethanolamine (PE), diphosphatidyl glycerol (DPG), phosphatidyl inositol (PI) and total phospholipid phosphorus. These observations demonstrate impaired phospholipid metabolism, probably at the biosynthetic level. The mitochondrial oxidation of long-chain fatty acids was also impaired after Mg depletion. Mg depletion (serum Mg fell 60%) also resulted in significant falls in myocardial [ATP], phosphocreatine (PCr), and Mg with a concomitant rise in myocardial Ca content. These observations are consistent with the tenet that prolonged low [Mg2+]zero can result in marked reduction in oxygen and substrate delivery to the cardiac myocytes, with concomitant changes in membrane phospholipids (potentially resulting in a pro-oxidant state) probably as a result of coronary vasoconstriction.