Epitestosterone, or isotestosterone, also known as 17α-testosterone or as androst-4-en-17α-ol-3-one, is an endogenous steroid and an

epimer In stereochemistry, an epimer is one of a pair of diastereomers. The two epimers have opposite configuration at only one stereogenic center out of at least two. All other stereogenic centers in the molecules are the same in each. Epimerization i ...

of the

androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This in ...

sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effect ...

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristi ...

. It is a weak

competitive Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indivi ...

antagonist of the androgen receptor (AR) and a potent

5α-reductase inhibitor 5α-Reductases, also known as 3-oxo-5α-steroid 4-dehydrogenases, are enzymes involved in steroid metabolism. They participate in three metabolic pathways: bile acid biosynthesis, androgen and estrogen metabolism. There are three isozymes of ...

. Structurally, epitestosterone differs from testosterone only in the configuration at the hydroxy-bearing carbon, C17. Epitestosterone is believed to form in a similar way to testosterone; a 1993 study found that around 50% of epitestosterone production in human males can be ascribed to the testis, although the exact pathway of its formation is still the subject of research. It has been shown to accumulate in mammary cyst fluid and in the

prostate The prostate is both an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found only in some mammals. It differs between species anatomically, chemically, and phys ...

. Epitestosterone levels are typically highest in young males; however, by adulthood, most healthy males exhibit a testosterone to epitestosterone ratio (T/E ratio) of about 1:1.

Society and culture

Detection of athletic doping

It has been shown that

exogenous In a variety of contexts, exogeny or exogeneity () is the fact of an action or object originating externally. It contrasts with endogeneity or endogeny, the fact of being influenced within a system. Economics In an economic model, an exogeno ...

administration of

does not affect levels of epitestosterone in the body. As a result, tests to determine the ratio of testosterone to epitestosterone in

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellular ...

are used to find athletes who are doping. A study of Australian athletes found that the mean T/E ratio in the study was 1.15:1. Another study found that the max T/E ratio for the 95th percentile of athletes was 3.71:1, and the max T/E ratio for the 99th percentile was 5.25:1. Epitestosterone has not been shown to enhance athletic performance, although administration of epistestosterone can be used to mask a high level of testosterone if the standard T/E ratio test is used. As such, epitestosterone is banned by many sporting authorities as a masking agent for testosterone.

Notable cases

A 1989 report by a committee of the Australian Senate claimed that "there is hardly a medal winner at the

1980 Moscow Olympics The 1980 Summer Olympics (russian: Летние Олимпийские игры 1980, Letniye Olimpiyskiye igry 1980), officially known as the Games of the XXII Olympiad (russian: Игры XXII Олимпиады, Igry XXII Olimpiady) and commo ...

, certainly not a gold medal winner...who is not on one sort of drug or another: usually several kinds. The Moscow Games might well have been called the Chemists' Games". A member of the IOC Medical Commission, Manfred Donike, privately ran additional tests with a new technique for identifying abnormal levels of testosterone by measuring its ratio to epitestosterone in

. Twenty percent of the specimens he tested, including those from sixteen gold medalists would have resulted in disciplinary proceedings had the tests been official. The results of Donike's unofficial tests later convinced the IOC to add his new technique to their testing protocols. In 1996 the US athlete Mary Decker failed a T/E test with a T/E ratio of greater than 6, the limit in force at the time. She took the case to arbitration, arguing that birth control pills can cause

false positive A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resul ...

s for the test, but the arbitration panel ruled against her. On September 20, 2007 Floyd Landis was stripped of his title as winner of the

Tour de France The Tour de France () is an annual men's multiple-stage bicycle race primarily held in France, while also occasionally passing through nearby countries. Like the other Grand Tours (the Giro d'Italia and the Vuelta a España), it consists ...

, and was subjected to a two-year ban from professional racing after a second test showing an elevated T/E ratio. Landis won the 17th stage of the tour; however, tests taken immediately after the stage victory showed a T/E ratio of 11:1, more than double the 4:1 imposed limit (recently lowered from prior limits of 8:1 and 6:1). On August 1, 2006, media reports said that synthetic testosterone had been detected in the A sample, using the carbon

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...

ratio test CIR. The presence of synthetic testosterone means that some of the testosterone in Landis's body came from an external source and was not naturally produced by his own system. These results conflict with Landis's public speculation that it was a natural occurrence. Landis originally denied the charges, but in 2010 Landis admitted to doping during much of his career, but continued to adamantly deny taking testosterone that would have led to the positive test in the 2006 Tour de France.

References

External links

Landis has T/E ratio twice the tour limit
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Clenbuterol – An In-Depth Look
{{Androgen receptor modulators 5α-Reductase inhibitors Androstanes Steroidal antiandrogens World Anti-Doping Agency prohibited substances

Society and culture

Detection of athletic doping

Notable cases

See also

References

External links