Observations on ADP aggregation of lithium chloride incubated platelets in a variety of mammalian species.

In citrated platelet-rich plasma of eight mammalian species lithium produces species-dependent effects on ADP aggregation ranging from stimulation to inhibition. Raising the extracellular calcium concentration enhanced aggregation of both lithium-stimulated and lithium-inhibited platelets, indicating that the extracellular calcium concentration has no direct relation to the effect of lithium on platelet function. Lithium did not induce changes in total intracellular platelet calcium and magnesium contents. Aggregation of platelets with ionophore A23187 showed the same species-specific lithium effects as aggregation induced by ADP. The data suggest that lithium does not exert its effect on platelets through interference with intra- or extracellular calcium concentrations.