In vitro effects of trace elements on blood clotting and platelet function. B--Zinc and magnesium.

The in vitro effects of zinc and magnesium salts on blood coagulation mechanism and platelet aggregation were studied on rat plasma. Addition of zinc sulphate to pooled rat plasma in a range of concentrations (0.3-1 mg/ml) caused a dose dependent significant prolongation of recalcification, prothrombin and partial thromboplastin times. These effects reached a peak after 30 minutes while the thrombin clotting time was not significantly altered and was even shortened in the presence of highest concentration of zinc tested (1 mg/ml). Incubation of thrombin with zinc sulphate (150 micrograms/ml) for up to 30 minutes did not affect significantly the action of thrombin. Incubation of the same concentrations of zinc sulphate with fibrinogen produced non clotting of fibrinogen after 0-minutes. Addition of rising concentrations of zinc sulphate to rat PRP produced inhibition of ADP-induced platelet aggregation. On the other hand, collagen-induced aggregation was insignificantly inhibited in the presence of zinc. In contrast, in vitro additions of rising concentrations of magnesium sulphate (2-5 mg/ml) to pooled rat plasma exerted no effect on recalcification time immediately after addition (0-minutes), but after 5 minutes following incubation it produced significant shortening of recalcification time in all the doses tested. The prothrombin time showed a general trend of shortening, maximal after 5-minutes incubation. The results of partial thromboplastin times revealed clotting before addition of calcium chloride. The thromboplastin time also showed progressive shortening with rising concentrations of magnesium sulphate. When thrombin solution was exposed to magnesium sulphate (2.5 mg/ml) no effect on the activity of thrombin was seen for up to 30 minutes. Fibrinogen solution similarly exposed to the same concentration of magnesium sulphate did not show any significant effect on its clottability with thrombin for up to 30 minutes. Magnesium sulphate in the range of doses tested significantly enhanced platelet aggregation of PRP in response to both ADP and collagen, and the responses observed were not dose dependent. The mechanisms underlying the effects of these two metals on blood clotting and platelet aggregation are discussed.