Lack of correlation between "in vitro" and "in vivo" antithrombotic activity of heparin fractions and related compounds. Heparan sulfate as an antithrombotic agent "in vivo"

The anticoagulant (U.S.P., APTT; "in vitro" and "in vivo") antithrombotic (aXa; Yin and Wessler and chromogenic), antilipemic (LPL) activities of heparin, heparin fractions and fragments, heparinoids, heparan sulfate and other sulfated glycosaminoglycans were compared with the activities of these compounds as antithrombotics "in vivo" by four different methods (vena cavae ligature, kaolin, collagen and steel coil). A lack of correlation was observed between the activities "in vitro" and the antithrombotic activity "in vivo". For instance heparan sulfate which shows negligible pharmacological activities "in vitro" is a potent antithrombotic agent "in vivo". Likewise, several heparin fractions and fragments have low aXa activity "in vitro" and high antithrombotic activity "in vivo". It is concluded from these results that the "in vitro" tests used cannot predict the antithrombotic activity "in vivo".