title: High-dose heparin suppresses platelet alpha granule secretion.
abstract: Platelet degranulation has been implicated in the pathophysiology of acute arterial thrombosis, intimal hyperplasia, and atherogenesis. Most previous studies that examined the effect of heparin on platelet function have used platelet aggregometry. These studies have resulted in contradictory data and, by the nature of the assay, reveal no information with regard to platelet degranulation. In contrast, flow cytometry allows accurate quantification of the extent of platelet degranulation by measurement of the platelet surface binding of a GMP-140 specific monoclonal antibody (S12). GMP-140 is only expressed on the platelet surface after platelet alpha granule release. In the present study increasing concentrations of heparin were added to whole blood anticoagulated with sodium citrate. Platelets were activated with a panel of agonists, and the extent of platelet degranulation was quantified by whole blood flow cytometry. Heparin concentrations as high as 100 units/ml were found to suppress platelet alpha granule release induced by either a thromboxane A2 analog (U46619) or a combination of adenosine diphosphate and epinephrine. Heparin suppressed alpha granule release induced by thrombin both in whole blood and in washed platelets. The addition of heparin after platelet activation had no effect on S12 binding. In summary, heparin in high concentrations is a potent inhibitor of platelet degranulation, an action that is unrelated to its effect on the coagulation cascade. Although the heparin concentrations used in this study exceed those used clinically by a factor of 10 or more, future studies of heparin fractions may allow the separation of the anticoagulant and antiplatelet properties of the molecule and allow the administration of an agent that selectively suppresses platelet degranulation without the humoral anticoagulant effect.
authors.affiliation: Division of Vascular Surgery, University of Massachusetts Medical School, Worcester 01655.
authors.forename: M J
authors.initials: MJ
authors.lastname: Rohrer
authors.forename: A S
authors.initials: AS
authors.lastname: Kestin
authors.forename: P A
authors.initials: PA
authors.lastname: Ellis
authors.forename: M R
authors.initials: MR
authors.lastname: Barnard
authors.forename: L
authors.initials: L
authors.lastname: Rodino
authors.forename: W L
authors.initials: WL
authors.lastname: Breckwoldt
authors.forename: J M
authors.initials: JM
authors.lastname: Li
authors.forename: A D
authors.initials: AD
authors.lastname: Michelson
mesh_terms: D000244:Adenosine Diphosphate / Q000037:antagonists & inhibitors; D000818:Animals; D000911:Antibodies, Monoclonal; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D015550:Cell Degranulation / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000037:antagonists & inhibitors; D005434:Flow Cytometry; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D019007:P-Selectin; D010980:Platelet Membrane Glycoproteins / Q000032:analysis; D011450:Prostaglandin Endoperoxides, Synthetic / Q000037:antagonists & inhibitors; D013917:Thrombin / Q000037:antagonists & inhibitors
chemical_list: D000911:Antibodies, Monoclonal; D019007:P-Selectin; D010980:Platelet Membrane Glycoproteins; D011450:Prostaglandin Endoperoxides, Synthetic; D000244:Adenosine Diphosphate; D006493:Heparin; D013917:Thrombin; D004837:Epinephrine