Abstract

Five mucopolysaccharide stains inhibit platelet aggregation induced by several aggregating agents: with two stains inhibition is competitive. Alcian blue, 0·05 mg/ml, added to platelet-rich plasma potentiates ADP-induced aggregation. Alcian blue, 0·5 mg/ml, itself produces platelet aggregation, probably causing the release reaction. Three of these stains produce aggregation of red cells. They also bind heparin, and so may influence heparin-neutralizing sites (platelet factor 4) and probably the charge on the platelet membrane. The only known common factor to these stains is their ability to bind onto the mucopoly-saccharides. It is suggested that when platelets are `stained' the surface mucopolysaccharide is altered and that this alteration can influence platelet aggregation.