Molecular weight dependence of the anticoagulant properties of heparin: Intravenous and subcutaneous administration of fractionated heparins to man |
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Authors: | D.A. Lane I.R. MacGregor M. VanRoss G. Cella V.V. Kakkar |
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Affiliation: | Thrombosis Research Unit, King's College Hospital Medical School, Denmark Hill, London SE5, U.K. |
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Abstract: | A commercial mucosal heparin preparation has been fractionated by gel filtration into five different MW fractions of approximate mean MWs 11500–21500. These five heparins were randomly administered to 5 normal volunteers by intravenous and subcutaneous injection. The anticoagulant effects of the fractions were then determined by KCCT, anti-Xa clotting and anti-Xa chromogenic substrate assays. Following intravenous injection the high MW fraction produced identical elimination curves in all three assays, but with decreasing MW there was a divergence between results obtained by KCCT and anti-Xa assays. The lowest MW fraction produced between 2–3 times greater heparin levels when measured by anti-Xa assay. This divergence in assay results was produced as a consequence of the differences in specific activities seen when fractionated heparins were assayed in vitro by the different assay methods. That is, low MW heparin fractions had a higher anti-Xa specific activity than that determined by the KCCT assay. Conversely, high MW heparin had a greater specific activity when determined by the KCCT assay. When the response to intravenous heparin injection (measured by KCCT and anti-Xa assays) was compared to the dose administered it was found that the anti-Xa response was greater than expected. This increased plasma heparin like activity was not dependant upon the MW of the heparin fractions, and could not be neutralised by PF4. A MW dependance was observed for the absorption of the heparin fractions into the circulation following subcutaneous injection, with low MW heparin producing higher heparin levels determined by all the assays. |
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