title: Platelets interact with fibrin only after activation.
abstract: Interactions between platelets and fibrin have been visualized by phase contrast, epifluorescence, and scanning electron microscope examination of clots formed with dansylcadaverine-labeled fibrin and gel-filtered platelets. After thrombin activation, the platelets appeared as fluorescent aggregates with bridging strands of fibrin; formaldehyde-fixed platelets were not fluorescent under the same experimental conditions. Scanning electron micrographs demonstrated that thrombin-activated cells had numerous pseudopods to which the fibrin strands adhered; fixed platelets exhibited a smooth discoid appearance and did not interact with the clot. Platelets trapped in clots formed with Batroxobin (Pentapharm) (platelets are not activated by Batroxobin as confirmed by light-scattering aggregometry measurements) remained as nonfluorescent, discoid cells, whereas platelets first activated by adenosine diphosphate formed brightly fluorescent aggregates. Light-scattering data of thrombin activation (0.2 U/mL) indicated that preincubation of platelets with 0.1 mmol/L prostaglandin E1 (PGE1) prior to addition of thrombin decreased the extent and rate of platelet shape change and resulted in 100-fold slower aggregation. Clots formed in the presence of PGE1 revealed decreased fluorescence intensity and fewer platelet-fibrin contacts. Gly-Pro-Arg-Pro, which blocks fibrinogen binding and fibrin assembly, was also effective in blocking platelet-fibrin interactions. These results indicate that platelet activation is a prerequisite for attachment of platelets to fibrin.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D000527:Alprostadil; D012103:Batroxobin / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D011464:Epoprostenol / Q000494:pharmacology; D005337:Fibrin / Q000502:physiology*; D005338:Fibrin Fibrinogen Degradation Products; D006801:Humans; D008027:Light; D008855:Microscopy, Electron, Scanning; D008856:Microscopy, Fluorescence; D009842:Oligopeptides / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D011458:Prostaglandins E / Q000494:pharmacology; D012542:Scattering, Radiation; D013917:Thrombin / Q000494:pharmacology
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; D009842:Oligopeptides; D011458:Prostaglandins E; C011468:fibrinmonomer; D000244:Adenosine Diphosphate; C034585:glycyl-prolyl-arginyl-proline; D005337:Fibrin; D011464:Epoprostenol; D012103:Batroxobin; D013917:Thrombin; D000527:Alprostadil