Summary
Magnesium (Mg) has shown the ability to inhibit arterial thrombus formation in some
experimental animal studies. This effect may be due to an inhibition of platelet reactivity
as in vitro studies have demonstrated that Mg inhibits platelet aggregation. In order
to evaluate the in vivo effect of Mg in humans measurements of platelet activity,
fibrinolytic activity, as well as measurements of prostacyclin (PGI2), and nitric oxide (NO) release were performed after infusion of magnesium sulphate
(MgSO4) in healthy volunteers. In a placebo controlled, cross-over study in 14 healthy male
subjects, 8 mmol MgSO4 was given as an intravenous bolus over 15 min followed by 3 mmol MgSO4/h.
The mean S-Mg concentration increased from 0.85 to 1.50 mM during the Mg infusion
period. A transient decrease in blood pressure was observed during the initial bolus
infusion of Mg. Haemodynamic parameters were otherwise stable. The bleeding time increased
by 48% during the Mg infusion (p <0.005), and in accordance with this, ex vivo platelet
aggregation in platelet rich plasma was significantly inhibited, both following collagen
(p = 0.02) and ADP (p = 0.04) stimulation. There were no significant changes in plasma
beta-thromboglobulin concentration or the excretion of 2,3-dinor-thromboxane B2 in
the urine. Neither tissue plasminogen activator (t-PA)activity, tissue plasminogen activator (t-PA)antigen nor plasminogen activator inhibitor (PAI)antigen changed during the Mg infusion period. There was no sign of increased release of
PGI2 from the vessel wall as judged by urinary concentration of 2,3-dinor-6-keto-prostaglandin
F1α. Nor was there any sustained increase in the release of NO, measured as nitrate concentration
in urine. However, a transient increase in NO release was observed during one sample
period.
In conclusion a reduced platelet activity and increased bleeding time, was found during
Mg infusion in healthy volunteers. Fibrinolytic activity showed no changes. An anti-platelet
effect may in part be responsible for the beneficial effect of Mg, described in patients
with acute myocardial infarction (MI) and preeclampsia.
