Polymorphonuclear leukocytes (PMN) when activated release products that can potentially injure endothelial cells or alter endothelial function. Exposure of cultured human umbilical vein endothelial cells to cathepsin G and elastase isolated from human PMN at concentrations reached in vivo (100 ng/mL to 10 micrograms/mL) selectively inhibited thrombin-induced prostacyclin production and the thrombin-induced rise in cytosolic free calcium ([Ca++]i) concentration. These proteases also blocked thrombin-induced release of arachidonic acid from prelabeled endothelial cells (EC). In contrast, induction of prostacyclin (PGI2) production by arachidonate, histamine, or the calcium ionophore A23187 was not altered by treatment of EC with these proteases. The effects of the proteases were concentration-dependent, were blocked by serum or serum protease inhibitors, and were reversed when the endothelial cells were further cultured for 24 hours in the absence of the proteases. Elastase, but not cathepsin G, also produced detachment of endothelial cells. Thus, the major leukocyte proteases selectively suppress thrombin-induced prostacyclin production by human vascular endothelial cells and may alter the hemostatic balance at sites of PMN activation.

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