Inhibition of agonist-induced platelet aggregation by magnesium sulfate warrants its use as an alternative in vitro anticoagulant in pseudothrombocytopenia.

MgSO is effective in preventing spontaneous in vitro platelet agglutination in anticoagulant-induced pseudothrombocytopenia (PTCP). In order to learn more about its potential as an in vitro anticoagulant, platelets from MgSO-anticoagulated blood were stimulated by several differentially-acting agonists (ADP, ARA, TRAP, epinephrine, collagen and ristocetin). Platelet aggregation in blood samples from 11 and 17 volunteers was measured by light-transmission aggregometry (LTA) according to Born and impedance aggregometry (Multiplate), respectively. Agonist-induced platelet aggregation was markedly lower in MgSO-anticoagulated samples when compared with citrate-anticoagulated samples (decrease of 95.75% (ristocetin), 69.02% (collagen) and 75.73% (epinephrine)) or hirudin-anticoagulated samples (decrease of 85.99% (ADP), 80.98% (ARA), 77.24% (ristocetin), 54.37% (collagen) and 50.14% (TRAP)). The anti-aggregatory effect of MgSO is dose-dependent and readily detectable at a concentration of 7.5 mmol/l. Analysis of the agonist signaling pathways suggest that MgSO interferes with the final step of platelet aggregation, namely the intracellular mobilization of Ca.