EPO induction of EPOR, eNOS, and NO in HUAECs. (A) EPO (▪) in combination with low oxygen tension (2% O₂) increased EPOR expression in primary HUAECs compared with no EPO (□) at 21% O₂ (^*P < .05). Results were normalized to β-actin expression. (B) In the absence of EPO, expression of eNOS at 2% O₂ was less than one-half of the value under normoxia. However, EPO (solid bars) reversed the decrease in eNOS expression at low oxygen tension. Results were normalized to β-actin expression. (C) NO production was measured in HUAECs as released nitrite after one hour of stimulation with EPO (5 U/mL) (▪) and without EPO (open bars). L-NAME (▨) suppressed the EPO response. Error bars represent SD.