Circulating Platelet Aggregates Indicative of in Vivo Platelet Activation in Pulmonary Hypertension

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Abstract
The authors investigated the existence of circulating cellular aggregates in 12 patients with moderate to severe pulmonary hypertension, using scanning elec tron microscopy. Peripheral venous blood was collected in the presence of 11.5 mM buffered ethylenediaminetetraacetic acid, in order to disperse freshly formed disaggregable aggregates. Irreversible aggregates represented by plate let clusters and/or platelet attachment to either leukocytes or red cells were identified in 7 patients with pulmonary hypertension. Endogenous platelet acti vation was further confirmed by a significant increase in plasma levels of beta- thromboglobulin in comparison with controls (33.8 ± 14.1 vs 22.7 ± 11.5 ng/mL respectively, p < 0.025). The presence of irreversible aggregates in the blood stream strongly suggests that cell-cell interactions actually occur in vivo in these patients. If so, therapeutic measures aimed at preventing in situ thrombosis and its consequences may be beneficial in this disorder.