Adrenaline Activates Human Platelets But Does Not Cause Primary Aggregation If Thrombin Generation Is Inhibited By Hirudin

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Abstract
Adrenaline(ADR) affects human platelets(PLAT) by binding to a receptors,inhibiting adenylate cyclase and translocating Ca2+ across the plasma membrane. In citrated PLAT-rich plasma(CIT-PRP), ADR induces primary aggregation(1stAGG), which may be followed by 2ndAGG due to the activation of the arachidonate(AA) pathway and the release(REL) of ADP. ADR acts synergistically with other aggregating agents. In contrast, ADR does not aggregate suspensions of washed human PLAT(SWHP) and hirudin(HIR)-PRP. To determine the role of traces of thrombin(THR) on AGG and REL of 14C-5HT of prelabeled PLAT induced by ADR,we have used SWHP and PRP anticoagulated with CIT(13mM), HIR(30 U./ml) or both and examined the effects of addition of HIR(30 U./ml),a specific inhibitor of THR. ADR(1-10μM) does not cause AGG or REL of SWHP,even in the presence of added HIR or CIT. However, ADR(1-10μM) potentiates the effects of ADP and AA on AGG and REL. This is not inhibited by HIR. THR alone (0.02 U./ml) causes shape change of SWHP,addition of ADR(4.5μM) causes extensive AGG and REL, which are inhibited by HIR.In CIT-PRP, ADR(1-10μM)causes 1st AGG followed by 2ndAGG and REL, addition of HIR to CIT-PRP has no effect on AGG and REL. Aspirin(ASA) and/or CP/CPK inhibit 2ndAGG-induced by ADR in CIT-PRP. Addition of ASA+CP/CPK+HIR does not inhibit ADR-induced 1stAGG in CIT-PRP. After addition of CIT to HIR-PRP, ADR does not AGG PLAT. In contrast, ADP causes 1stAGG without REL in HIR-PRP and addition of CIT to HIR-PRP induces 2ndAGG and REL. However, ADR causes 1stAGG and REL, if PRP was prepared from blood to which HIR has been added at the same time of CIT or later. In conclusion: 1) ADR does not cause 1stAGG in SWHP or HIR-PRP if the PLAT have not been exposed to THR during their isolation; 2) traces of THR change the response of PLAT to ADR independently of the effect of CIT on Ca2+ concentrations; 3) the use of CIT-PRP does not prevent completely THR generation.

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