The effects of heparin, protamine, and heparinase 1 on platelets in vitro using whole blood flow cytometry

The effects of heparinization and the reversal of heparin activity on plate let function after cardiopulmonary bypass have not been well defined. Flow cytometry has become a convenient and powerful technique for characterizing platelets. We examined the expression of a secretion marker (P-selectin) a nd an aggregation marker (activated fibrinogen receptor GP IIb-IIIa) on nor mal platelets in response to heparin, heparinase 1, and protamine in vitro using whole blood flow cytometry. Unfractionated heparin increased adenosin e diphosphate-induced expression of P-selectin and GP IIb-IIIa in a dose-de pendent manner. Heparinase 1 alone deceased both markers of platelet activa tion. Protamine alone increased P-selectin expression but had no effect on GP IIb-IIla expression. Heparinase 1 antagonized the stimulatory effect of heparin on both markers. In contrast, protamine antagonized the effect of h eparin on GP IIb-IIIa expression but potentiated the effect of heparin on P -selectin expression, Those in vitro observations suggest that 1) both hepa rin and its reversal agents affect platelet secretion and aggregation, and 2) heparinase 1 reverses heparin-induced platelet preactivation more effect ively than protamine. Implications: This experimental in vitro study demons trates that heparin and its reversal agents affect platelet secretion and a ggregation.