Actinoidin, like vancomycin, inhibits ristocetin-and ristomycin-induced VIIIR:WF-dependent agglutination of untreated or formaldehyde-fixed human platelets but does not interfere with bovine factor VIII-induced agglutination. The socalled "direct effect" of ristocetin and ristomycin on fixed platelets, which is represented by an immediate increase in light absorbancy in the absence of cofactor, was not blocked by actinoidin at concentrations which totally inhibited agglutination in the presence of VIIIR:WF. Actinoidin does not inhibit thrombin-induced platelet aggregation. This represents a further argument against a common platelet membrane receptor site for thrombin and ristocetin or a ristocetin-VIIIR:WF complex on the platelet membrane.
- platelet agglutination inhibitor
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