Definition of Erythropoietin (EPO)

Erythropoietin (EPO)A hormone the kidneys produce that stimulates the bone marrow to increase red blood cell production. Erythropoietin is a protein structure called a cytokine.

Specialized cells in the renal cortex, called peritubular fibroblasts, respond to the amount of oxygen in the blood as it passes through the kidney. When the oxygen saturation of the blood is low (hypoxia), the peritubular fibroblasts increase EPO production.

Normally the bone marrow releases about two million erythrocytes into circulation every minute. The EPO stimulates the bone marrow to release higher numbers of erythrocytes into the blood circulation, which boosts the amount of hemoglobin and increases the blood’s capacity to carry oxygen.

Erythropoietin production falters in serious kidney disease, resulting in anemia. Medications that diminish kidney function may have similar effects. The liver and perhaps other sites in the body also produce small amounts of erythropoietin, though not enough to meet the body’s needs when the kidneys fail. Some people experience fluctuations in erythropoietin production, both increases and decreases, after kidney transplantation.

EPO Side Effects

During the 1980s researchers identified and sequenced the gene responsible for EPO, allowing the synthesis of recombinant erythropoietin in the laboratory. Administered by injection, this form of EPO, epoetin alpha (Procrit, Epogen), can supplement or replace endogenous EPO to stimulate the bone marrow when kidney production falls off or other circumstances cause rapid erythrocyte depletion and corresponding anemia.

Potential side effects of EPO supplementation include increased blood pressure (hypertension) especially when the cause of anemia is renal failure, and thrombosis (the formation of blood clots within the blood vessels) resulting from the increased percentage of erythrocytes in the blood.

See also BLOOD DOPING; CYTOKINESHEMATOPOIESISMULTIPLE MYELOMA.

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