Thrombus formation in vivo

To examine thrombus formation in a living mouse, new technologies involving intravital videomicroscopy have been applied to the analysis of vascular windows to directly visualize arterioles and venules.After vessel wall injury in the microcirculation, thrombus development can be imaged in real time.These systems have been used to explore the role of platelets, blood coagulation proteins, endothelium, and the vessel wall during thrombus formation.The study of biochemistry and cell biology in a living animal offers new understanding of physiology and pathology in complex biologic systems. History of the study of hemostasis and thrombosisThe study of blood coagulation and thrombosis has moved through many stages.The classic studies of thrombus morphology and pathology were followed by a period in which blood coagulation proteins were identified based on the characterization of patients with hereditary clotting disorders.The fundamentals of platelet physiology, including platelet adhesion and aggregation, were defined by turbidimetric assay reporting platelet-platelet interaction and the adherence of platelets to glass beads, which reflects the ability of platelets to stick to surfaces that mimic the injured vessel wall.Only 40 years ago were the techniques of protein biochemistry applied to the study of hemostasis and thrombosis.Proteins were purified, their amino acid sequences determined, their genes isolated, and their interaction with other components analyzed in vitro.Protein domain structures were defined and their functional and structural relationship to other protein families determined.Site-specific mutagenesis and definition of the molecular basis of hemophilia identified functionally critical amino acids.From the analysis of the many enzymes, cofactors, structural proteins, ligands, and receptors involved in hemostasis and thrombosis, descriptive models emerged that explained the in vitro experimental results and the in vivo clinical observations in humans (1).These models have changed over the years, with continued refinement based on new information and fresh thinking (2-9).Still, many questions remain.We have learned what reactions and interactions can happen in vitro, but we need to understand what does happen in vivo.We are entering a new phase of discovery -the study of thrombosis in living animals to understand the mechanisms involved in this complex system.