Background Angiotensin Ⅱ type 1 receptor (ATR1) / Angiotensin Ⅱ type 2 receptor (ATR2) usually interact with each other in their expression and physiological functions, and nitric oxide (NO) is always involved in ATR1 / ATR2 regulation in vivo. Endothelial cells play a crucial role in the maintenance of vascular function and in the prevention of cardiovascular diseases. Objectives To investigate the effects of angiotensin Ⅱ (Ang Ⅱ) and ATR1 blocker valsartan on ATR1, ATR2 expression and their relation with endothelial nitric oxide synthase (eNOS) expression, and NO production in cultured vascular endothelial cells. Methods Human umbilical vein endothelial cell line (HUVEC) and bovine aortic endothelial cell (BAEC) were used. BAEC were isolated from aorta of newborn calf by enzyme digestion and cells of 3-5 passages were used. Cells were incubated with vehicle, Ang Ⅱ, valsartan, or Ang Ⅱ plus valsartan respectively for various periods. ATR1, ATR2, eNOS expression and NO production were detected. Results Incubation with AngⅡ or valsartan apparently downregulated ATR1 mRNA and protein expression in vascular endothelial cells, and the combination effect of the two drugs were more apparent. Ang Ⅱ showed a transient slightly promotive effect on eNOS and NO generation in BAEC and an apparently inhibitory effect with prolonged incubation, while valsartan can apparently reverse those effects. Conclusions Both Ang Ⅱ and valsartan downregulated the expression of ATR1 in vascular endothelial cells. The synergistic effect of the two drugs was more apparent. Prolonged incubation with Ang Ⅱ can apparently inhibit eNOS expression and NO production in endothelial cells, while valsartan can apparently reverse that inhibitory effect. Background Angiotensin Ⅱ type 1 receptor (ATR1) / Angiotensin Ⅱ type 2 receptor (ATR2) interact interact with each other in their expression and physiological functions, and nitric oxide (NO) is always involved in ATR1 / ATR2 regulation in vivo. Objectives To investigate the effects of angiotensin II (Ang II) and ATR1 blocker valsartan on ATR1, ATR2 expression and their relation with endothelial nitric oxide synthase (eNOS) expression , and NO production in cultured vascular endothelial cells. Methods Human umbilical vein endothelial cell line (HUVEC) and bovine aortic endothelial cell (BAEC) were used. BAEC were isolated from aorta of newborn calf by enzyme digestion and cells of 3-5 passages were used. Cells were incubated with vehicle, Ang Ⅱ, valsartan, or Ang Ⅱ plus valsartan respectively for various periods. ATR1, ATR2, eNOS expression and NO prod Uction were detected. Results Incubation with Ang II or valsartan apparently downregulated ATR1 mRNA and protein expression in vascular endothelial cells, and the combination effect of the two drugs were more apparent. Ang II showed a transient slightly promotive effect on eNOS and NO generation in BAEC and an apparently inhibitory effect with prolonged incubation, while valsartan can apparently reverse those effects. Conclusions Both Ang Ⅱ and valsartan downregulated the expression of ATR1 in vascular endothelial cells. The synergistic effect of the two drugs was more apparent. Prolonged incubation with Ang Ⅱ can apparently inhibit eNOS expression and NO production in endothelial cells, while valsartan can apparently reverse that inhibitory effect.