Activation of platelet cyclooxygenase by red cells in vitro.

Detectable amounts of products of the platelet cyclooxygenase pathway, such as thromboxane A2 and malondialdehyde, have been found in vivo, suggesting that platelets are activated in the circulation. The mechanisms by which platelets might be activated in vivo are not yet clear. Evidence has been provided that adenosine diphosphate released by red blood cells could have a role in inducing in vivo platelet aggregation. This finding prompted speculation that red cells could also continually liberate adenosine diphosphate in vivo, thus activating platelets.