Hormone, erythropoietin

Erythropoietin is a substance produced by the kidney that leads to the formation of red blood cells in the bone marrow. Abbreviated: EPO. The kidney cells that make EPO are specialized and are sensitive to low oxygen levels in the blood coming into the kidney. These cells release erythropoietin when the oxygen level is low in the kidney. Erythropoietin stimulates the bone marrow to produce more red blood cells which in turn increases the oxygen-carrying capacity of the blood. EPO is the prime regulator of red cell production. Its major functions are to promote the differentiation and development of red blood cells and to initiate the production of hemoglobin, the molecule within red cells that transports oxygen. EPO is produced not only in the kidney but also, to a lesser extent, in the liver. The EPO gene has been found on human chromosome 7 (in band 7q21). Different DNA sequences flanking the EPO gene act to control liver versus kidney production of EPO. The measurement of EPO in the blood can indicate bone marrow disorders or kidney disease. Normal levels of EPO are 0 to 19 mU/ml (milliunits per milliliter). Elevated levels can be seen in polycythemia rubra vera, a disorder characterized by an excess of red blood cells. Lower than normal values of EPO are seen in chronic renal failure. Using recombinant DNA technology, EPO has been synthetically produced for use in persons with certain types of anemia: anemia due to kidney failure, anemia secondary to AZT treatment of AIDS , and anemia associated with cancer. EPO has been much misused as a performance-enhancing drug in endurance athletes such as reportedly cyclists (in the Tour de France), long-distance runners, speed skaters, and Nordic (cross-country) skiers. When misused in such situations, EPO is thought to be especially dangerous (perhaps because dehydration can further increase the viscosity of the blood, increasing the risk for heart attacks and strokes. EPO has been banned by the Tour, the Olympics, and other sports organizations.