Summary
The effects on platelet function of temperatures attained during hypothermia used
in cardiac surgery are controversial. Here we have performed studies on platelet aggregation
in whole blood and platelet-rich plasma after stimulation with a range of concentrations
of ADP, TRAP, U46619 and PAF at both 28°C and 37°C. Spontaneous aggregation was also
measured after addition of saline alone. In citrated blood, spontaneous aggregation
was markedly enhanced at 28°C compared with 37°C. Aggregation induced by ADP was also
enhanced. Similar results were obtained in hirudinised blood. There was no spontaneous
aggregation in PRP but ADP-induced aggregation was enhanced at 28°C. The P2Y12 antagonist AR-C69931 inhibited all spontaneous aggregation at 28°C and reduced all
ADP-induced aggregation responses to small, reversible responses. Aspirin had no effect.
Aggregation was also enhanced at 28°C compared with 37°C with low but not high concentrations
of TRAP and U46619. PAF-induced aggregation was maximal at all concentrations when
measured at 28°C, but reversal of aggregation was seen at 37°C. Baseline levels of
platelet CD62P and CD63 were significantly enhanced at 28°C compared with 37°C. Expression
was significantly increased at 28°C after stimulation with ADP, PAF and TRAP but not
after stimulation with U46619. Overall, our results demonstrate an enhancement of
platelet function at 28°C compared with 37°C, particularly in the presence of ADP.
Keywords
ADP - aggregation - hypothermia - platelet activation - platelets
