Effects of prolonged recombinant human erythropoietin administration on muscle membrane transport systems and metabolic marker enzymes.

Adaptations to chronic hypoxia involve changes in membrane transport proteins. The underlying mechanism of this response may be related to concomitant occurring changes in erythropoietin (Epo) levels. We therefore tested the direct effects of recombinant human erythropoietin (rHuEpo) treatment on the expression of muscle membrane transport proteins. Likewise, improvements in performance may involve upregulation of metabolic enzymes. Since Epo is known to augment performance we tested the effect of rHuEpo on some marker enzymes that are related to aerobic capacity. For these purposes eight subjects received 5,000 IU rHuEpo every second day for 14 days, and subsequently a single dose of 5,000 IU weekly for 12 weeks. Muscle biopsies were obtained before and after 14 weeks of rHuEpo treatment. The treatment increased hematocrit (from 44.7 to 48.8%), maximal oxygen uptake by 8.1%, and submaximal performance by approximately 54%. Membrane transport systems and carbonic anhydrases involved in pH regulation remained unchanged. Of the Na(+), K(+)-pump isoforms only the density of the alpha2 subunit was decreased (by 22%) after treatment. The marker enzymes cytochrom c and hexokinase remained unchanged with the treatment. In conclusion, changes in muscle membrane transport proteins and selected muscle enzymes do not contribute to the Epo-induced improvement in performance.