Short-term rhEpo treatment increases L ferritin and total iron content in skeletal muscle; long-term rhEpo treatment decreases muscle L ferritin. The figure shows the changes in the ferritin and iron content of muscle biopsy samples obtained from the vastus lateralis before and after 8 and 28 days of rhEpo treatment. The ferritin heavy (H) and light (L) subunit contents (A) were determined by ELISA with the use of monoclonal antibodies against the corresponding recombinant human ferritin subunits and are expressed in relation to their pretreatment values, arbitrarily defined as 100. The values are all representative of 3 independent determinations. Total iron content (B) was determined by atomic absorption spectrometry, measured in μg/100 mg dry weight and expressed in relation to its pretreatment value, arbitrarily defined as 100. Values are mean plus or minus SE for 8 participants. (C,D) Complementary experiments involving independent groups of participants (see “Methods”). (C) Values are mean muscle ferritin levels plus or minus SE measured in 4 participants before and 10 hours after the injection of a single rhEpo dose of 15000 IU (complementary experiment B). (D) Values are mean muscle ferritin levels plus or minus SE measured in 8 participants before and after 14 weeks of rhEpo treatment, expressed in relation to the pretreatment value, arbitrarily defined as 100 (complementary experiment A). The statistical differences from pre-rhEpo values were calculated with the Wilcoxon test; *P < .05; ‡P = .05.