Exposure of heparin-bearing anticoagulant materials to whole blood, plasma, or serum has been shown to lead to partial elution of heparin. Similar effects are obtained when graphite-bensalkonium-heparin (GBH) or poly-4-vinylpyridine-heparin (PVPyrH) surfaces are exposed to bovine plasma protein fractions. Loss of heparin from these anticoagulant materials appears to be dependent on the nature of the cationic surface and on the particular protein fraction used. With whole blood and plasma, and with most of the protein fractions studied, it was found that a larger fraction of the original heparin was eluted from GBH than from PVPyrH. Surfaces exposed to bovine Cohn fraction IV lost considerably more heparin than similar surfaces exposed to Cohn fractions I, 11, 111, or V, and fraction V removed less than the others, a t the same or higher concentrations, and less from PVPyrH than from GBH.
The elution of heparin from anticoagulant surfaces has been of interest, and continues to be of interest, both for the elucidation of mechanism of action of these surfaces and for the very practical objective of preparing longer-lasting heparinized materials. It has been recognized for some time that heparin, ionically bound to cationic nitrogen compounds such as benzalkonium, is lost more rapidly on exposure to whole blood or plasma than on exposure to distilled water or isotonic saline solutions.
Whiff en and Gott' found that not only heparin but also benzalkonium is lost from GBH (graphite-benzalkonium-heparin) surfaces. The authors implanted polycarbonate rings coated with GBH, containing 14C-benzalkonium, into the inferior vena cava of dogs. Rings were removed over a 6 month period and analyzed for I4C. Whiffen and Gott found that the benzalkonium u-as eluted a t an exponential 107