Human umbilical vein endothelial cells blocked platelet serotonin release and aggregation in response to thrombin doses up to 0.5 U/mL via an aspirin-insensitive EDRF/NO mechanism.
Does EDRF/NO from human endothelial cells inhibit human platelet reactivity?
EDRF/NO formation from L-arginine by human endothelial cells acts as an aspirin-insensitive fluid-phase inhibitor of human platelet reactivity.
To determine a role for endothelium-derived relaxing factor/nitric oxide (EDRF/NO) in regulation of human platelet reactivity by human endothelial cells (EC), we studied combined suspensions of human umbilical vein endothelial cells (HU-VEC, passage 2 through 3) and washed human platelets. Confluent HUVEC monolayers were treated with aspirin (1 mmol/L) to prevent prostacyclin (PGI2) formation, washed, and harvested. Aspirin-treated platelets alone (58 x 10(6)) were fully aggregated by thrombin at 0.05 U/mL or more. In the presence of 10(6) HUVEC, however, platelet serotonin release and aggregation in response to thrombin at doses as high as 0.5 U/mL were blocked. We demonstrated for the first time that inhibition of aggregation and serotonin release, due to EDRF/NO, occurred in parallel. HUVEC-dependent inhibition of platelet responsiveness was enhanced by superoxide dismutase (SOD) and reversed by hemoglobin. The inhibitory effect was also reversed by preincubation of HUVEC with NG-monomethyl-L-arginine (NMA) or NG-nitro-L-arginine (NNA) through competitive blockade of arginine metabolism. Pretreatment of platelets with methylene blue indicated that EC-dependent inhibition of platelet reactivity occurred through activation of platelet soluble guanylate cyclase. When platelets and HUVEC were separated by a permeable membrane and both cells were stimulated by thrombin, platelets remained unresponsive. This indicated that inhibition was induced by a fluid-phase mediator, independent of direct cell-cell contact. These data demonstrate that EDRF/NO formation from L-arginine by human EC plays an important role as an aspirin-insensitive fluid-phase inhibitor of human platelet reactivity.
Broekman et al. (Thu,) conducted a other in Platelet reactivity. Human umbilical vein endothelial cells (HUVEC) suspension vs. Platelets alone was evaluated on Platelet serotonin release and aggregation in response to thrombin. Human umbilical vein endothelial cells blocked platelet serotonin release and aggregation in response to thrombin doses up to 0.5 U/mL via an aspirin-insensitive EDRF/NO mechanism.