Modifications of platelet shape change and ATP release during cardiopulmonary bypass

Platelet activation is accompanied by characteristic morphological changes: smooth-disc platelets become more spherical in shape and develop psudopods. The purpose of this study is to investigate whether platelets change after extracorporeal bypass. Twenty-two patients undergoing cardiopulmonary bypass (CPB) were studied prior to anesthesia and immediately after the operation. Platelets activated by different agonists were monitored simultaneously for morphological changes, ATP release and aggregation. While shape change measured before surgery was large, it was significantly reduced after bypass surgery (p < 0.01); morphological changes were quicker postoperatively. Several other parameters also changed: the time lapse between administration of the agonist and the start of ATP secretion decrease significantly (p < 0.01). After activation with high concentrations of ADP, ATP release was significantly increased (p < 0.01). On the other hand, less ATP was released after platelet activation with collagen and arachidonic acid, suggesting a change in platelet adhesion or a downregulation of endoperoxide synthesis. In our study, the importance of preactivation change in shape, estimated quantitatively by percent loss in ability of changing shape, can be compared using various agonists, with proportional defects in release and aggregation. These data provide evidence for different intrinsic levels in platelet defects after CPB.