Magnesium inhibits human platelets.

Magnesium (Mg) may inhibit experimental arterial thrombus formation by inhibition of platelet activity. However, inhibition of platelet aggregation has mainly been shown with high concentrations of magnesium ( > 2 mM). To test the effects of Mg in more clinically relevant concentrations, an in vitro study was performed where platelets were incubated with MgSO4 in the concentration range of 0.5-8.0 mM. Healthy volunteers participated on 2 consecutive days. On Day 2 the volunteers ingested 300 mg of acetylsalicylic acid (ASA) 1 h before blood sampling. Blood was anticoagulated with hirudin and platelet aggregation was performed in platelet-rich plasma (PRP) after incubation with saline or MgSO4 for 5 min. Platelets were stimulated with threshold concentrations of collagen or ADP or a fixed high concentration of collagen (5 micrograms/ml) on both days. A concentration dependent inhibition of platelet aggregation was found after addition of MgSO4. A statistically significant inhibition (P < 0.05) was present at 0.5-1.0 mM MgSO4. The effect of Mg was independent of pretreatment with ASA. Following maximal stimulation with collagen in PRP, a synergistic inhibition of ASA and Mg on platelet aggregation was demonstrated. Administration of MgSO4 in clinically relevant concentrations showed a dose-dependent inhibition of platelet aggregation. Platelet inhibition also occurred after ASA administration and concomitant medication induced a synergistic effect.