Measurement of NO production in endothelial cells during incubation with hydroxyurea and 2 other cytostatic agents. (A) HUVECs were treated with different concentrations of hydroxyurea (10 and 20 μM). (B) TrHBMECs, as well as HUVECs, were treated with different concentrations of hydroxyurea. (C) HUVECs were treated with different concentrations of butyric acid sodium salt (0.5 and 1 mM) and 5-azacytidine (10 and 20 μM). (D) TrHBMECs were treated with the same concentrations of butyric acid sodium salt and 5-azacytidine as HUVECs. Results are from 3 to 4 independent experiments: HUVECs are from different cryopreserved cells pooled from several donors, whereas TrHBMECs are thawed from a new cryovial for each experiment. Values are mean ± SEM (n = 3).