Answer:
decreased production of EPO by their kidneys.
Explanation:
Erythropoietin (EPO) is a peptide hormones that can be produced synthetically by recombinant DNA technology. It increases red blood cells in athletes thereby increasing their aerobic capacity.
The protein is also synthesised by the kidneys. High level of oxygenation inhibits it's synthesis, while renal tissue hypoxia promotes production.
Since intake of synthetic EPO raises oxygen levels, it will reduce the production by the kidneys.
