Interactions between stimulated platelets and endothelial cells in vitro.

Prostaglandins and hydroxy acids are synthesized mainly from the essential polyunsaturated fatty acid arachidonate, and these substances have been identified in almost all mammalian tissues. Prostaglandins, thromboxane A2 (TXA2) and prostacyclin (PGI2) are autocoids that appear to function in the regulation of vascular tone, cell secretion and contractile processes. So far, hydroxy acids have been found to function as chemotactic agents and in the formation of slow-reacting substances. Other actions of hydroxy acids will certainly be defined in future research. The endoperoxides PGG2 and PGH2 represent common precursors of all prostaglandin end-products. In studying the prostaglandin metabolism of a specific tissue, the total profile of endoperoxide transformation should be determined. In platelets the endoperoxides are transformed mainly into TXA2, a potent vasoconstrictor and inducer of platelet aggregation. Endothelial cells convert endoperoxides to PGI2, a vasodilator and inhibitor of platelet aggregation. In addition, endothelial cells can utilize endoperoxides from stimulated plates to form PGI2. The concept that platelets and endothelial cells can share common precursors for the production of modulating substances may be applicable to other cell types.