Endothelium-derived relaxing factor inhibits thrombin-induced platelet
aggregation by inhibiting platelet phospholipase C
W Durante, MH Kroll, PM Vanhoutte and AI Schafer
Medical Service, Houston VA Medical Center, TX 77030.
Endothelium-derived relaxing factor (EDRF) inhibits platelet function, but
the mechanism underlying this inhibitory effect is not known. To examine
this, cultured acetylsalicylic acid (ASA)-treated endothelial cells (EC)
from bovine aorta (BAEC) or from human umbilical vein (HUVEC) were
incubated with washed, ASA-treated human platelets. Incubation of platelets
with either BAEC or HUVEC resulted in inhibition of thrombin-induced
platelet aggregation that was dependent on the number of EC added. This
effect was potentiated by superoxide dismutase and reversed by treating EC
with NG-nitro-L-arginine or by treating platelets with methylene blue,
indicating that the inhibition of platelet aggregation was due to the
release of EDRF by EC. EC significantly blocked the thrombin stimulated
breakdown of phosphatidylinositol-4,5-bisphosphate (PIP2) and the
production of phosphatidic acid in [32P]orthophosphate-labeled platelets
and of inositol trisphosphate in [3H]myoinositol-labeled platelets. In
addition, the thrombin-mediated activation of protein kinase C (PKC) and
phosphorylation of myosin light chain were inhibited in the presence of EC.
Finally, thrombin stimulated an increase in cytosolic ionized calcium
concentration ([Ca2+]i) in fura2-loaded platelets that was abolished by
concentrations of EC which also blocked thrombin- induced aggregation.
These data indicate that EDRF blocks thrombin- induced platelet aggregation
by inhibiting the activation of PIP2- specific phospholipase C and thereby
suppressing the consequent activation of PKC and the mobilization of
[Ca2+]i.
Volume 79,
Issue 1,
pp. 110-116,
01/01/1992
Copyright © 1992 by The American Society of Hematology
