Botrocetin (venom coagglutinin): reaction with a broad spectrum of multimeric forms of factor VIII macromolecular complex.

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Abstract
Botrocetin, originally called venom coagglutinin, is a Bothrops factor that causes aggregation of [human] blood platelets in the presence of the von Willebrand component of the factor VIII macromolecular complex. The complex consists of a series of multimers with a MW of .apprx. 1-20 .times. 106. Ristocetin, another agent that causes platelet aggregation dependent on von Willebrand factor, reacts with only the higher MW multimers. The reactivity of botrocetin in relation to the multimeric structure of the factor VIII complex is reported. Several plasmas or plasma fractions with abnormal distribution of the multimeric sizes were examined, including variant von Willebrand disease type IIA with lack of the higher MW forms, commerical antihemophilic factor concentrates with a preponderance of lower MW forms, cryoprecipitate-free plasma containing mainly the smaller multimers, and a chromatographic fraction of plasma containing only the highest MW polymers. Factor VIII-related antigen content was adjusted to 25-100%. All of the preparations lacking the high MW forms caused prompt platelet aggregation with botrocetin, but none of them caused aggregation in the ristocetin test made isochronal with the botrocetin test. The very high MW polymers were equally effective with botrocetin and ristocetin. These findings indicate that the Bothrops factor is reactive with a broad spectrum of high to low MW forms of the factor VIII complex; this suggests that bioassays of von Willebrand factor with botrocetin should correlate better with immunoassays for factor VIII-related antigen and could reflect better the full platelet-aggregating function of the complex than do ristocetin determinations.