Characterization of a new hereditary thrombopathy in a closed colony of Wistar rats

A new hereditary thrombopathy has been identified in a closed colony of Wistar rats. A simple and reproducible cuticle bleeding time test was developed as a rapid screening procedure for the bleeding diathesis. Affected animals exhibit markedly prolonged bleeding times and complete absence of platelet aggregation either with adenosine diphosphate (ADP) or with thrombin. Inheritance data suggest an autosomal dominant inheritance pattern with variable penetrance. Coagulation tests, platelet counts, plasma von Willebrand factor (vWF) activity, and clot retraction are within normal limits in thrombopathic animals. GPIb-dependent botrocetin-induced platelet agglutination was present in washed thrombopathic rat platelets. No discernible abnormality of intraplatelet organelles or granules was seen by transmission electron microscopy of thrombopathic platelets. A qualitative morphologic assessment of intraplatelet fibrinogen in thrombopathic rat platelets showed no discernible difference as compared with control rat platelets. Thrombopathic rat platelets exhibit decreased glycoprotein IIb/IIIa (GPIIb/IIIa) antigen by flow cytometric analysis and markedly decreased iodine 125-labeled fibrinogen binding to platelet GPIIb/IIIa after ADP activation. This rat colony demonstrates a unique thrombopathy, distinct from previously described animal thrombopathies, with some characteristics of variant Glanzmann's thrombasthenia. This animal model may provide further insight into the regulatory mechanisms and pathophysiology of platelet GPIIb/IIIa.