The role of heparin on platelet retention by acrylonitrile co-polymer dialysis membranes.

The role of heparin on platelet--foreign surface interactions was examined by platelet retention studies on acrylonitrile--dimethylaminoethyl methacrylate (AN-DMAEMA) dialysis membranes both with and without the bonding of heparin onto their surfaces. Heparin bonding significantly reduced platelet retention. Heparin in solution (4 units/ml.) increased platelet retention when the surface of the membranes was modified by ethylene oxide but had no significant effect on the platelet-retaining properties of unmodified membranes. Studies using heparin 99mTc demonstrated that unmodified membranes took up heparin from solution whereas ethylene oxide-modified membranes had little such affinity. The heparin bonding process greatly increased the heparin uptake achieved by simple soaking in heparin solution, and the leaching rate was less than 1% at 70 hours. The results indicate that heparin has two antagonistic effects in this platelet-foreign surface interaction: it acts directly on platelets to increase adhesiveness while acting on the foreign surface to reduce platelet retention.