Non-isotopic method for quantitation of platelets and erythrocytes in experimental thrombi

Experimental animal models of thrombosis have been established in several species to examine factors responsible for thrombotic disorders in man. One technical facet of all thrombosis models is the need to quantitate cell deposition on thrombogenic surfaces, and this is routinely accomplished with radioisotopic labeling of specific components. Data reported here demonstrate that formalin-fixed thrombi can be hydrolyzed with chymotrypsin allowing recovery and quantitation of platelets and erythrocytes incorporated within the clot. Recovery of platelets from in vitro generated, model thrombi averaged 99 +/- 10% (mean +/- 1 SD; n = 7; range 88-116%) of calculated content; recovery of erythrocytes was 94.1 +/- 1.1% (n = 6) as measured by recovery of cellular hemoglobin after chymotrypsin hydrolysis of clots. Chymotrypsin was also shown to release platelets and erythrocytes from string-bound thrombi generated in vivo with an arterio-venous shunt model in beagle dogs. Platelet recovery from these string clots after chymotrypsin hydrolysis was independently verified with a quantitative Western blot assay of platelet antigens. These data demonstrate that experimental thrombi can be hydrolyzed with chymotrypsin, thereby not only eliminating the need for radioisotopes, but also permitting flow cytometric analysis of cells comprising the thrombus.