EPO induction of NO in HUVECs. (A) NO production was measured in HUVECs as released nitrite after one hour of stimulation by EPO (5 U/mL) (▪) and compared with no EPO (□) (^*P < .05). L-NAME suppressed the EPO response (▨). (B) In HUVECs cultured at 2% O₂, EPO induction of NO was observed within 30 minutes with a maximal effect at 5 U/mL. Error bars represent SD.