The idea of ​​a "hormone" was not well received by the scientific community, and it was a difficult concept to describe, because scientists did not Were not familiar with the idea of ​​a chemical substance. messengers influencing the actions of body cells. Many scientists, such as Arnold Adolph Berthold, Thomas Addison, Joseph von Mering and Oskar Minkowski, George Murray, as well as George Oliver and Edward Albert Schäfer, conducted experiments studying the role of endocrine glands and their chemical messengers. However, their fellow scientists believed that the nervous system was responsible for the results of their experiments, not the chemical messengers (hormones) of the endocrine system. It was not until 1902 that two scientists, William Bayliss and Ernest Starling, demonstrated the mechanism of the hormone secretin and its ability to cause the secretion of bicarbonate in the form of pancreatic juice from the pancreas into the duodenum during digestion. Following this discovery, endocrinology was recognized as an official branch of science, and these famous chemical messengers that so many scientists attempted to corroborate were eventually defined as hormones. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”?Get the original essayA hormone is now understood to be a chemical messenger, released in very small quantities by a cell, which exerts a biological action on a cell target. Erythropoietin (EPO) is a well-known hormone today. In 1906, Paul Carnot and Clotilde-Camille Deflandre proposed the existence of a “humoral factor” regulating erythropoiesis after observing an increase in red blood cells in rabbits after injecting them with anemic blood. Decades later, KR Reissman and Allan Erslev exploited Carnot and Deflandre's discoveries and improved their experiment, thus convincing the scientific community of the existence of a chemical messenger playing a crucial role in erythropoiesis. In 1977, Eugene Goldwasser and his team purified and isolated this chemical messenger. Over the years that scientists studied this factor, it was called hematopoietin, erythropoietic stimulating factor, etc., until it was finally accepted as "erythropoietin" (American Society of Hematology) . EPO is a 165 amino acid glycoprotein with two disulfide bonds. , which is produced mainly in the kidneys and, to a lesser extent, in the liver. The exception to this rule is before birth and in people with loss of kidney function. In both cases, the main site of EPO synthesis is the liver. In the kidney, erythropoietin is synthesized by peritubular fibroblasts of the renal cortex. Secretion of EPO by peritubular fibroblasts stimulates erythropoiesis (production of red blood cells) in the bone marrow. EPO production depends on tissue oxygen levels: lower oxygen levels increase EPO production and secretion and high oxygen levels decrease EPO production and secretion. EPO has several targets and functions in the body. EPO has its effects on erythroid cells, non-erythroid cells and non-erythroid tissue/organ systems. Specifically, EPO acts in the bone marrow, causing athletes to overuse its effects, in neurological development, in heart tissue, in the intestines, in angiogenesis, and it acts to improve obesity . As mentioned previously, EPO stimulates erythropoiesis in the bone marrow. This occurs in response to a low hematocrit, or the ratio of red blood cells in the blood to the total amount of bloodin the body. Low red blood cell counts mean low blood oxygen levels, because red blood cells carry oxygen throughout the bloodstream. Low tissue oxygen levels can be the result of the body having to replace red blood cells (due to a 120-day lifespan), shortened red blood cell lifespan, blood loss, low production of red blood cells or diseases such as anemia (low oxygen levels in the tissues). level of blood cells or hemoglobin in the blood). The kidneys are stimulated to release EPO in response to the hypoxia-inducible transcription factor complex, which regulates EPO release. This factor is highly expressed under conditions of low oxygen content and poorly expressed under conditions of high oxygen content. When the hypoxia-inducible transcription factor complex is expressed, EPO is released by the kidney and causes differentiation of erythroid progenitors in the bone marrow, by binding to the EPO receptor on these cells. This causes an increase in hematocrit and therefore an increase in the oxygen carrying capacity of the blood. Due to the fact that EPO increases the levels of red blood cells in the blood, and therefore the oxygen carrying capacity of the blood, EPO is highly sought after by athletes for the purpose of engaging in "doping". blood”. Blood doping involves athletes taking synthetic EPO to enhance their performance because they will have an increased oxygen capacity in their blood. However, many athletes do not realize that taking high doses of EPO causes oxidative stress, which results in an abundance of oxygenated free radicals in the body, flooding the body's antioxidants with more free radicals than they can absorb. can eliminate them. Free radicals have a negative effect on the body's cells, destroying many essential organelles and cellular components. Doping with EPO was therefore banned in professional sport. Regardless, many of today's athletes, both professional and non-professional, use EPO to improve their athletic abilities. EPO also plays a role in neurodevelopment. Specifically, when EPO is released by the kidney, it has a direct effect on neuroblastoma cells, forcing them to differentiate, and on oligodendrocytes, increasing their number. This fact was manifested in a study carried out on infants with cerebral palsy. Specifically, synthetic EPO has been shown to have curative effects on infants, acting as a neuroprotective factor. The same result resulted in another study involving subjects who had suffered an acute stroke. Administration of EPO to these subjects showed a reduction in stroke symptoms and an overall improvement in their condition. Additionally, a lack of EPO receptors in animal models, such as mice, resulted in a decrease in neural progenitor cells and apoptosis activity in the nervous system, indicating that EPO is necessary for the proper functioning and maintenance of neurons. Additionally, in studies performed in vivo, EPO has been shown to act, again, as a neuroprotective factor, protecting against brain damage. Additionally, EPO contributes to heart function. In an in vivo study in rats with myocardial infarction, EPO administration significantly reduced cardiomyocyte apoptosis, thereby strengthening cardiac function and increasing cardiac lifespan. EPO increases the probability of survival of endothelial cells against possible ischemic injury of.