Erythropoietin levels in EPAS1^+/– mice are not induced by hypoxia. (A) Renal erythropoietin mRNA levels for EPAS1^+/+ (□) or EPAS1^+/– (▦) mice exposed to room air (RA), short-term intermittent hypoxia (STIH), or short-term continuous hypoxia (STCH) (n = 4 per genotype per treatment group). Statistically meaningful differences in means between erythropoietin mRNA levels from EPAS1^+/+ or EPAS1^+/– mice after STIH exposure (one-tailed t test with P = .07) or STCH exposure (one-tailed t test with P = .06) are indicated with an asterisk. (B) HIF-1α, HIF-2α, or actin protein levels as assessed by Western blot analyses of nuclear extracts from representative EPAS1^+/+ (+/+) or EPAS1^+/– (+/–) mice maintained under RA, STIH, or STCH conditions. A nonspecific (NS) band seen with use of the HIF-2α monoclonal antibody is indicated for comparison between samples. (C) Hematocrit levels for EPAS1^+/+ (□) or EPAS1^+/– (▦) mice maintained at RA (n = 21 per genotype), STIH (n = 22 per genotype), or STCH (n = 13 per genotype). Statistically meaningful difference in means between the hematocrit levels of EPAS1^+/+ or EPAS1^+/– mice maintained at RA is indicated with an asterisk (one-tailed t test with P = .01). (D) Hematocrit levels for EPAS1^+/+ (□) or EPAS1^+/– (▦) mice maintained at RA or after long-term continuous hypoxia (LTCH) exposure (n = 6 per genotype per treatment group). Statistically meaningful difference in means between the hematocrit levels of EPAS1^+/+ or EPAS1^+/– mice maintained at LTCH is indicated with an asterisk (one-tailed t test with P = .003). Values are expressed as the mean plus or minus standard error of the mean. (E) Erythropoietin protein levels as assessed by Western blot analyses of serum from representative EPAS1^+/+ (+/+) or EPAS1^+/– (+/–) mice maintained under room air (RA) or medium-term continuous hypoxia (MTCH) conditions. The same membrane was reprobed for mouse serum IgG as a comparison between samples.