[Difference in inhibitory actions of products of the myeloperoxidase- catalyzed reaction on initial aggregation of activated platelets].

Inhibition of the initial aggregation of isolated rabbit platelets was studied on two types of their stimulation. The stimuli were either ADP, which was also capable to induce cell rounding, or adrenaline, and CaCl2, which acted without cell rounding. When platelets are stimulated by adrenaline or calcium chloride, sodium hypochlorite enhances the anti-aggregatory effect: at a concentration of about 10 microM the aggregation is reduced by 50%. This inhibitory effect is 1.5-3 times the ADP-stimulated inhibition of the aggregation of platelets or the inhibition of platelet aggregation by N-chloralanine under activation of platelets by any stimulus. Dithionitrobenzoic acid, which is a widely used reactant for sulfhydryl groups, also suppresses the platelet aggregation. Its inhibitory effect is similar to the of antiaggregatory action of sodium hypochlorite on platelets. It is not excluded that the enhanced antiaggregatory effect of sodium hypochlorite is due to an alteration of calcium channels in platelet plasma membranes, which occurs with the involvement of sulfhydryl groups.