Stimulatory effects of endotoxin on the platelet secretory process

The effects of the lipopolysaccharides (LPS) of Proteus mirabilis (smooth a nd rough types), differing significantly in their composition on the releas e of compounds stored in specific platelet granules, were studied. There ar e two main types of secretory granules in blood platelets. Dense granules c ontain adenine nucleotides, and in alpha-granules different proteins are st ored. The LPS were found to cause a dose-dependent release of proteins and adenine nucleotides. In the extracellular medium LDH activity was not prese nt. The results presented in this study indicate that LPS from P. mirabilis act directly on blood platelets and induce the platelet secretory process. In comparison with thrombin, a strong platelet agonist, the action of the endotoxins tested was weak.