Magnesium in arterial thrombosis, ischaemia-reperfusion injury, and atherosclerosis - evidence from experimental studies

摘要

Magnesium is a trace mineral with an atomic number of 12 and a mass of 24.32 Dalton. It is the fourth most abundant cation in the body and the second most abundant cation in intracellular fluid. Magnesium is an important cofactor for more than 300 enzymatic reactions involving energy metabolism and protein synthesis (Elin, 1994). It is also involved in several processes including: gating of calcium channels, transmembrane ion flux and regulation of adeny-late cyclase, muscle contraction, control of vasomotor tone, and cardiac excitability (Fawcett et al, 1999). In many of the cardiovascular effects magnesium reflect an antagonism of calcium-initiated processes, which has led to the characterisation of magnesium as "nature's physiological calcium blocker" (Iseri and French, 1984). In humans magnesium is distributed principally between bone (53%) and intracellular compartments of muscle (27%) and soft tissues (19%); and less than 1% is found in serum and red blood cells (Elin, 1994). Only approximately 0.3% of total body magnesium is found in serum, where it is present in three states: 1) free ionised magnesium (62%; the physiologically active form), 2) protein bound (33%; mainly albumin), and 3) complexed to anions (5%; such as citrate and phosphate). Sources rich in magnesium include, grain, cereals, and vegetables and the absorption occurs principally in the ileum and colon. The amount absorbed is inversely correlated to the intake. Excretion and serum magnesium control occur via the kidney (Fawcett et al, 1999). Assessment of magnesium status is a complex area as the ion is predominantly located intracellularly. Description of the laboratory tests available for total body magnesium measurement is beyond the scope of this review (see ref. Elin, 1994). The intention of the present work is to summarise the pharmacological effects of magnesium on the cardiovascular system, particularly the potential antithrom-botic and the myocardial protective effect. In this respect magnesium should be seen as a therapeutic substance, where treatment is given irrespective of the actual magnesium status in the individual.