PLATELET-FUNCTION IN ACUTE ISCHEMIC STROKE - RELEVANCE OF GRANULE SECRETION

We studied platelet aggregation and secretion in 48 patients with isch emic stroke, within 24 h of onset of symptoms, and 17 healthy controls . Aggregation was studied in platelet-rich plasma with the impedance m ethod. As markers of dense and alpha-granule secretion we used adenosi ne triphosphate (ATP) and platelet factor 4 (PF4), respectively. Furth ermore, we determined the basal platelet serotonin levels as an indica tor of previous in vivo platelet activation. Platelet aggregation and secretion of ATP and PF4 were significantly increased in the patients in response to 1.0 and 2.0 mu g/ml collagen. Similarly, the patients e xhibited significantly increased platelet aggregation and PF4 secretio n induced by 1.0 and 10 mu mol/l adenosine diphosphate. Platelet aggre gation in response to 1.0 mu mol/l of platelet-activating factor was s imilar in patients and controls, but the parallel ATP secretion was si gnificantly higher in patients. Platelets in patients thus exhibited a n enhanced responsiveness to all three agonists, suggesting a general lower threshold for activation. The basal platelet levels of serotonin were significantly decreased in patients, indicating a previous in vi vo platelet activation. Our data suggest that platelets are hyperaggre gable with an increased secretion in the acute phase of cerebral infar ct. Apart from the established importance of platelet hyperaggregabili ty in clot formation, platelet hypersecretion of serotonin and a-granu le proteins may be of significance in the pathophysiology of ischemic stroke.