 - Nitric oxide Nitric oxide NO; endothelium-derived relaxing factor is an inhibitor of platelet aggregation that is produced by endothelial cells and platelets. Studies in uremic patients have shown that platelet NO synthesis is increased and that uremic plasma stimulates NO production by cultured endothelial cells. The increase in NO synthesis may be due to elevated levels of guanidinosuccinic acid, a uremic toxin that may be a precursor for nitric oxide in this setting. 