Epinephrine enhances platelet aggregation at the expense of procoagulant activity

Objective Platelet activation is characterized by shape change, granule secretion, activation of fibrinogen receptor (glycoprotein [GP] IIb/IIIa) sustaining platelet aggregation, and externalization of negatively-charged aminophospholipids contributing to platelet procoagulant activity. Epinephrine alone is a weak platelet activator. However, it is able to potentiate platelet activation initiated by other agonists. Here, we investigated the role of epinephrine in the generation of procoagulant platelets.

Material and Methods Human platelets were activated with convulxin (CVX, the agonist of the collagen receptor GPVI), thrombin (THR) or Thrombin Receptor Activator for Peptide 6 (TRAP6, the agonist of the thrombin receptor PAR1), epinephrine (EPI), and combination thereof. Platelet aggregation was assessed by light transmission aggregometry or with PAC-1 binding by flow cytometry. Procoagulant COAT platelets, induced by combined activation with CVX-plus-THR, were visualized by flow cytometry as Annexin-V-positive and PAC-1-negative platelets. Cytosolic calcium fluxes were monitored by flow cytometry using Fluo-3 indicator.

Results EPI increased platelet aggregation induced by low doses of CVX alone, TRAP6 alone, and combined CVX+TRAP6. On the other hand, EPI dose-dependently reduced the formation of procoagulant COAT platelets generated by combined CVX+THR activation. We observed significant decrease (relative -10 %, p<0.05) of Annexin-V positivity and increase (relative +10 %, p<0.05) of PAC-1 binding with the triple activation (CVX+THR+EPI) compared with CVX+THR. Calcium mobilization with triple activation was decreased with the higher dose (1000 µM) compared with CVX+THR calcium kinetics.

Conclusion While CVX+THR induced the formation of procoagulant COAT platelets (express negatively charged phospholipids at their surface, and lose aggregatory properties), the addition of EPI (triple stimulation) modulated platelet activation reducing cytosolic calcium mobilization, decreasing the procoagulant response and enhancing platelet aggregation.

Publication History

Article published online:
18 June 2021