title: Ristocetin induces platelet aggregation: a morphological demonstration.
abstract: Changes in the morphology of human platelets induced by ristocetin in platelet-rich plasma (PRP) have been analysed at the ultrastructural level by means of a tannic acid procedure. Studies were also undertaken to measure the release of serotonin. Modifications of the aggregation tests induced by apyrase, a monoclonal antibody (Mab) to GPIIb/IIIa and by EDTA were also investigated. Transmission electron microscopy revealed that ristocetin precipitated adhesive proteins on the platelet membrane. An electron-dense deposit was seen within 20 s after ristocetin was added. When experiments were carried out in the aggregometer cuvette during stirring, groups of platelets became activated, changed their shape, and finally aggregated releasing part of their contents. The morphology of aggregates did not differ from those formed in the presence of ADP. Aggregation studies demonstrated that a Mab to GPIIb/IIIa modified the extent and the rate of the aggregation curve when RIPA was performed in citrated platelet-rich plasma (c-PRP), while apyrase modifies the extent, but not the slope, of the curve. Neither the antibody nor apyrase modified RIPA when it was performed in PRP obtained in the presence of EDTA. All this evidence suggests that RIPA in c-PRP, besides reflecting the interaction of GPIb with vWF, may also test other mechanisms of the platelet function including: assembly of GPIIb/IIIa complex, interaction of fibrinogen with this glycoprotein complex, and possibly the release reaction.
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D001081:Apyrase / Q000494:pharmacology; D001792:Blood Platelets / Q000648:ultrastructure*; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D008854:Microscopy, Electron; D010974:Platelet Aggregation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000276:immunology; D012310:Ristocetin / Q000494:pharmacology*
chemical_list: D000911:Antibodies, Monoclonal; D010980:Platelet Membrane Glycoproteins; D012310:Ristocetin; D004492:Edetic Acid; D001081:Apyrase