Objective      To determine the effect of erythropoietin (EPO) on the mitochondrial biogenesis in rat cardiomyocytes under the condition of chronic hypoxia.       Methods      Rat cardiomyocyte-derived H9c2 cells were deprived of oxygen for 7 d to establish the chronic hypoxia model (94% N

2

5%CO

2

and 1%O

2

). Then the obtained H9c2 cells were treated by recombinant human EPO (rhEPO

5

10 and 20 U/ml) for 3 or 7 d. Fluorescent probe was used to mark mitochondria in the cells for the amount of mitochondria. The protein levels of Akt

phospho-A

kt (serine473)

endothelial nitric oxide synthase (eNOS)

and phospho-eNOS (serine1177) were determined with Western blotting. RT-PCR was used to detect the relative copy number of mitochondrial DNA.       Results      rhEPO treatment for 7 d resulted in a significant increase in the amount and copy number of mitochondria (

P

0.05). The phosphorylation levels of Akt and eNOS were also enhanced

but those of akt and eNOS had no change (

P

0.05）.       Conclusion      EPO improves mitochondrial biogenesis in the cardiomyocytes exposure to chronic hypoxia

probably through Akt and eNOS signal transduction.