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This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Rights and Permissions Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Jesty, J. Search for Related Content PubMed PubMed Citation Articles by Jesty, J. Social Bookmarking                   What's this?  Previous Article  |  Table of Contents  |  Next Article  The kinetics of inhibition of thrombin by antithrombin in the presence of components of the hemostatic system J Jesty The inhibition of human thrombin by antithrombin has been measured in pure systems in the presence of other components of the hemostatic system that might affect the kinetics of the reaction. These included fibrinogen, calcium ions, phospholipid, prothrombin, platelets (both adenosine diphosphate [ADP]-stimulated and -unstimulated), and platelet extracts. Inhibition rates were measured in each case by a discontinuous amidolytic assay over a range of antithrombin concentrations, from 0 to 4.5 mumol/L. Under all conditions, rates of inhibition were proportional to antithrombin concentration. Calcium ions at 5 mmol/L caused a small (20%) reduction in rate, but phospholipid and prothrombin had no additional effect. In contrast, both fibrinogen and platelets significantly changed the rate of inhibition. In the presence of calcium, fibrinogen at concentrations from 0 to 12 mumol/L reduced the rate of inhibition in a competitive manner, giving an apparent Kd for fibrinogen of 6.0 mumol/L. As the plasma fibrinogen level is about 8 mumol/L, one may therefore predict that variations in fibrinogen level will have a significant effect on the rate of thrombin inhibition in plasma. More unexpected was the observation that platelets increase the rate of inhibition: unstimulated platelets increased the rate constant by 40%, and ADP- stimulated platelets increased it by 55%. However, this acceleratory effect could not be mimicked with either a KCI extract or a Triton extract of platelets, and its cause remains unknown. In sum, it has been shown that the rate of inhibition of thrombin can be modulated in at least three ways-antithrombin concentration, fibrinogen concentration, and platelets; each of which can vary independently in vivo. It is well known that defects of the first lead to an increased risk of thrombosis, and it is proposed that this may be substantially caused by changes in the kinetics of inhibition such as those described. Additionally, it is suggested that changes in inhibition rate caused by other components may also be significant, for the same reason, in modulating the clotting system in vivo. Volume 66, Issue 5, pp. 1189-1195, 11/01/1985 Copyright © 1985 by The American Society of Hematology CiteULike    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this? This article has been cited by other articles: T. G. Ruttmann Editorial II: Haemodilution enhances coagulation Br. J. Anaesth., April 1, 2002; 88(4): 470 - 472. [Full Text] [PDF]

	Copyright © 1985 by American Society of Hematology         Online ISSN: 1528-0020