The purpose of this study was an attempt to extrapolate favorable observations on the effects of magnesium on platelets and haemostasis from animal models to humans. Intravenous magnesium in the treatment of acute myocardial infarction has been tested in several large clinical trials and remains controversial. The mechanism for the cardioprotective properties of magnesium is unknown. Based on experimental studies, several different hypotheses have been advanced to explain the benefits of magnesium including it's effects on platelets and haemostasis. However, few studies have analysed such a relationship in humans. This project was designed to assess the effect of bolus magnesium infusion on ex vivo platelet aggregation and certain haemostatic parameters in healthy volunteers. One gram of magnesium was diluted in 50 ml of D5W and infused over a period of 15 min. The changes of platelet aggregability, plasma antithrombin-III, Protein C, total Protein S, fibronectin, endothelin-1, as well as the metabolites of thromboxane and prostacyclin were determined prior to and immediately after magnesium infusion. Results: Serum magnesium concentration increased from 2.10 ± 0.08 at baseline to 3.12 ± 0.13 mg dl-1 (P = 0.0002) post-infusion. Magnesium infusion was associated with a significant elevation in ADP (+19.3%); ristocetin (+13,6%); and collagen-induced platelet aggregation (+14.2%); an increase in plasma antithrombin-III (+10.3%) and thromboxane (+49.4%) when compared to pre-infusion levels. Against this, total Protein S (-20.7%), Protein C (-11.2%) and ET-1 (-26.3%) plasma concentrations were markedly decreased. There were no significant differences in plasma fibronectin and prostacyclin levels. Contrary to expectations, magnesium infusion in human volunteers is associated with platelet activation and mostly small unfavourable changes in certain haemostatic factors. However, the observed changes were small and for the most part remained within the normal physiologic range.
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