Stimulatory effects of endotoxin on the platelet secretory process.

The effects of the lipopolysaccharides (LPS) of Proteus mirabilis (smooth and rough types), differing significantly in their composition on the release of compounds stored in specific platelet granules, were studied. There are two main types of secretory granules in blood platelets. Dense granules contain adenine nucleotides, and in alpha-granules different proteins are stored. The LPS were found to cause a dose-dependent release of proteins and adenine nucleotides. In the extracellular medium LDH activity was not present. 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.