Analyses of anemia observed in kd/kd mice. (A) Peripheral blood from 3-month-old WT and kd/kd mice was analyzed. Erythrocytes (RBC), hemoglobin (Hb), hematocrit (Hct), leukocytes (WBC), and platelets (PLT) were determined (*P < .05, compared with WT). (B) The mRNA expression levels of HIF-1α (left panel) and HIF-2α (right panel) were examined in BM, spleen, kidney, and liver by quantitative RT-PCR. The expression levels seen in WT were normalized to a value of 1 as the standard in each tissue. ■ represents WT; □ represents kd/kd (**P < .01, compared with WT). (C) Epo protein levels in sera and hematocrit were analyzed after exposure to a low oxygen concentration (6%) for 48 hours. Peripheral blood was harvested 0, 48, 96, and 144 hours after starting the experiment. ■ represents WT; □ represents kd/kd. (D) The mRNA expression levels of Epo (top), HIF-1α (middle), and HIF-2α (bottom) were examined in kidney and liver by quantitative RT-PCR. RNA samples were collected from WT and kd/kd mice under normoxic (N) or hypoxic (H, 48-hour exposure to 6% O₂) conditions. The expression levels in WT kidneys at normoxia were normalized to a value of 1 as the standard. ■ represents WT; □ represents kd/kd (*P < .05 and **P < .01, compared with normoxic conditions). Error bars represent SD.