Protamine sulphate inhibits platelet membrane glycoprotein Ib-von Willebrand factor activity

Platelet adhesion to the injured vessel wall is essential in haemostasis an d thrombosis. This process involves the interaction of the platelet glycopr otein Ib (GPIb) with surface bound von Willebrand factor (vWF). Since synth etic polycationic peptides of the general formula (Arg)n, (Lys)n or (Arg-Ly s)n inhibit GPIb-vWF interaction, they were suggested as potential antithro mbotics. Protamine sulphate is a highly cationic polypeptide. arginine acco unting for approximately 60% of the primary sequence. utilized to neutraliz e the anticoagulant effect of heparin after cardiac surgery. We have invest igated potential effects of protamine sulphate on the function of GPIb-vWF. Addition of protamine sulphate to platelet-rich plasma (PRP). reduced signi ficantly the GPIb-vWF activity as assessed by ristocetin-induced platelet a gglutination. When protamine sulphate was added to PRP containing heparin. even at clinically relevant neutralizing doses the GPIb-vWF activity was re duced by 20-30% (p<0.001). Protamine sulphate in excess of heparin nearly a bolished the activity. Furthermore, the direct effect of protamine sulphate on collagen-induced platelet thrombus formation in non-anticoagulated huma n blood was investigated by employing an ex-vivo parallel-plate perfusion c hamber device. Protamine sulphate (200 mu g/mL) reduced platelet-collagen a dhesion at shear rates of 650 and 2600 sec(-1) by 40% (p<0.004) and 45% (p< 0.0001). respectively. The corresponding platelet thrombus volumes were con comitantly reduced by 90% (p<0.006) and 84% (p<0.05). Our data are questioning the rationale for empirical repetitive protamine s ulphate administration when so-called "heparin rebound" after cardiac surge ry is suspected. since protamine sulphate in excess of heparin may impair t he platelet GPIb-vWF interaction necessary for normal haemostasis.