Exaggerated platelet reactivity to physiological agonists in war veterans with posttraumatic stress disorder.

An association between traumatic stress and cardiovascular disease (CVD) is supported by various epidemiological studies. Platelet activation and binding of activated platelets to leukocytes contributes to the pathophysiology of CVD. Evidence of hyperactive sympathetic nervous system, altered expression of platelet α2-adrenoreceptors (α2AR), and altered platelet adenylate cyclase activity in patients with posttraumatic stress disorder (PTSD) suggest that platelet reactivity in PTSD may be altered as well. We tested whether platelet reactivity to increasing doses of adenosine-diphosphate (ADP), epinephrine (EPI), or their combination differs between war veterans with PTSD (n=15) and healthy controls (n=12). For this purpose, citrated whole blood was incubated with increasing concentrations of ADP (0.1, 1, 10μM), EPI alone (10nM, 100nM, 1000nM), or EPI (10nM, 100nM, 1000nM) in combination with 0.1μM ADP. A subset of samples was also incubated with 10μM yohimbine (YOH), α2AR antagonist, to distinguish receptor-specific effects. Platelet CD62P expression and formation of platelet–leukocyte aggregates (PLA) [platelet–monocyte (P–Mo), –lymphocyte (P–Ly), and –neutrophil (P–Ne) aggregates] were measured using three-color flow cytometry. Platelet reactivity was higher in war veterans with PTSD when compared to controls, as determined by greater CD62P expression and formation of PLA in response to ADP alone or in combination with EPI. Platelet reactivity also correlated with the severity of PTSD symptoms. Preliminary experiments with YOH indicate that stress-associated EPI elevations may contribute to platelet activation through a α2AR-dependent mechanism. The enhanced platelet reactivity observed in our study may be the underlying mechanism contributing to the development of CVD in PTSD patients.