The Use of Erythropoietin by Athletes
Erythropoietin is a glycoprotein that is produced primarily in the kidneys in adults and, to a lesser extent, in the liver. It behaves like a hormone, regulating the level of erythropoiesis, and keeping the RBC count within a narrow range
It is used widely in medicine as a treatment for a number of serious illnesses, ranging from types of anaemia, to the treatment of certain types of cancer, and also in the battle against AIDS. Unfortunately certain athletes, who will do anything to win, have realised its ergogenic benefits, and also the severity of its misuse.
Regulation of Erythropoietin Production.
In the kidneys, erythropoietin is produced in fibroblastoid interstitial cells in the inner renal cortex, while in the liver, the hormone is produced by both hepatocytes and interstitial fibroblastoid cells. Although a variety of growth factors influence erythroid progenitor cell proliferation, erythropoietin is the most important, and erythropoiesis cannot continue in its absence.
Among the haematopoietic growth factors, erythropoietin is one of few that behaves like a hormone. It is unique because its production, under normal circumstances, is controlled solely at the level of its gene, by tissue hypoxia and not by the absolute number of circulating erythrocytes.
Hypoxia is the sole physiologic stimulus for erythropoietin production, and an excess of oxygen suppresses its production but never completely.
Some facts about EPO. (Birchard K, Lancet 1998; 352: 42.)
· Neither age nor gender influences the plasma erythropoietin level,
· Plasma erythropoietin is constant in a given individual,
· Erythropoietin production is regulated at the level of its gene,
· Hypoxia is the only physiologic stimulus for erythropoietin production,
· There are no pre-formed stores of erythropoietin,
· There is only one form of circulating erythropoietin
Following production in the kidneys and liver, erythropoietin travels to the bone marrow to interact with specific haematopoietic progenitor cells where it maintains RBC production.
What evidence is there that people take erythropoietin?
There are two current tests for EPO abuse. Prior to these however was a Haematocrit count. If the count was too high then the athlete in question would not be allowed to compete, but there would be no ban, as the test didn't actually prove that they were taking an illegal substance. The first of the current tests is to check the urine for recombinant EPO (an artificial type made by drug companies). This can easily be overcome by stopping the administration of EPO two or three weeks prior to competition. This way, the high levels of EPO will be out of the system, yet the large benefits of it will last for a number of months.
The other test is a blood test. EPO injections produce high quantities of immature RBC's in the blood, but again this can be over come by knowing how long it takes the immature cells...