Endothelium as a modulator of platelet reactivity.

The pathways through which endothelial cells can modulate platelet reactivity (whether directly via the secretion of agents that affect platelet function or indirectly through the regulation of coagulation or vascular tone) are sufficiently varied and complex that the direction of individual reactions can be altered as the homeostatic balance requires--in other words, the balance can be shifted in favour of activation or inhibition depending on circumstances. For example, endothelium has the capacity to express pro- or anticoagulant activities, and to release or inactivate agents that either promote or inhibit platelet aggregation. The role of endothelial cells in modulating platelet function is important, complex and as yet poorly understood, but our understanding of the processes involved has advanced greatly over the past few years and continues to increase.