SSHA, a semi-synthetic heparin analogue belonging to the chondroitin family, was reported to induce considerable anti-Xa activity in vivo being practically inactive in vitro. In a study designed to elucidate further the in vivo effects of this drug, SSHA and sodium heparin from porcine intestinal mucosa were injected subcutaneously into six volunteers on separate occasions over a period of three days in a cross-over trial. Before injection and 2,4,6,8 hours afterwards, the heparin-like activity

more »

... was measured by means of the APTT, the anti -Xa clotting test and two chromogenic substrate assays. The results show that SSHA mediates both anti-Xa and antithrombin activities in vivo. A comparison between the effects of SSHA and heparin is problematical, due to the heterogeneity of different heparin preparations. Low doses of the analogue (45 mg s.c.) induce proportionally higher and longer lasting anti-Xa activities than higher doses (90 mg s.c.). In an attempt to identify the mediator involved in the anticoagulant activity induced by SSHA in vivo, antithrombin III AT III) was removed from a plasma sample of one the subjects obtaining SSHA injections by immunosorption using Sepharose IVb coupled with antibodies against AT III. The AT III free plasma obtained was found to be devoid of heparin-like activity in the anti-Xa clotting test but it maintained its anticoagulant activity in the APTT assay. When purified AT III was added to this plasma its anti-Xa activity was largely restored. In conclusion, the inhibitory effect of SSHA on coagulation seems to involve at least two mechanisms: a direct one which does not depend on AT III and an indirect one, induced in vivo and mediated by AT III.