Microvascular heparin-like species with anticoagulant activity.

Calf microvasculature was isolated from retina and cerebral gray matter. These preparations contained 0.048-0.060 U of heparin-like anticoagulant activity per gram of wet tissue. The retinal microvascular material contained no detectable mast cells. The anticoagulant potency of this product was associated solely with endothelial cells. This property appears to be due to a heparinlike proteoglycan since molecular species with biologic activity are precipitated with 10% (wt/vol) trichloroacetic acid and are destroyed by incubation with Flavobacterium heparinase. Furthermore, the above component functions in a manner virtually identical to heparin since approximately 60% of these species with anticoagulant activity bind to antithrombin-concanavalin A-Sepharose 4B, and only 15% of their biologic potency is expressed in the presence of antithrombin modified near the mucopolysaccharide binding domain. The cerebral microvascular tissue contained a trace subpopulation of mast cells (approximately 0.3%). The anticoagulant activity of this preparation is most probably associated with both endothelial cells and mast cells. However, complete separation of these two cellular elements has proven difficult with current methodology.