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A prohormone refers to a committed precursor of a hormone, usually having minimal hormonal effect by itself. The term has been used in medical science since the middle of the 20th century. Though not hormones themselves, prohormones amplify the effects of existing hormones. Examples of natural, human prohormones include proinsulin and pro-opiomelanocortin. For peptide hormones, the conversion process from prohormone to hormone typically occurs after export to the endoplasmic reticulum and often requires multiple processing enzymes. For example, proinsulin is processed by PC 1/2, PC 3, and carboxypeptidase E to afford insulin. Proamylin, which is cosecreted with proinsulin, this requires the above three factors and an amidating monoxygenase. Though commonly misdescribed as such, Vitamin D3 is not an example of a prohormone or a hormone.〔Reinhold Vieth, Why “Vitamin D” is not a hormone, and not a synonym for 1,25-dihydroxy-vitamin D, its analogs or deltanoids, Journal of Steroid Biochemistry & Molecular Biology 89–90 (2004) 571–573 http://www.direct-ms.org/pdf/VitDVieth/Vit%20D%20not%20a%20Hormone%20Vieth.pdf〕 The word prohormones has taken on a new sense due to the presence of specific oral medications designed for athletes to affect hormone levels. For small molecule hormones, the conversion is often one step, and is often used to regulate hormone levels. == Prohormones of testosterone and other androgenic steroids == In the last two decades, pro hormones have also been used by bodybuilders, athletes, and nonmedical users of anabolic steroids and other hormones to refer to substances that are expected to convert to active hormones in the body. The intent is to provide the benefits of taking an anabolic steroid without the legal risks, and to achieve the hoped-for benefits or advantages without use of anabolic steroids themselves. Many of these compounds are legal to manufacture, sell, possess and ingest eliminating the legal problems associated with schedule III anabolic steroids. The typical definition of "prohormone" includes a steroidal molecule that has the opposite molecular structure to testosterone on either the 3a/b position or the 17b position. Testosterone has a ketone group on the 3 carbon and a hydroxyl on the 17b carbon. A steroid with modifications away from testosterone in one or both of these areas is commonly referred to as a "prohormone". These enzymatic changes occur with the body's bidirectional enzymes.〔Lommer D, Dorfman RI, Forchelli E. Reversal of the 3 -hydroxysteroid dehydrogenase-isomerase reactions in rat adrenals. Steroidologia. 1970;1(3):175-82.〕〔WARD MG, ENGEL LL. REVERSAL OF THE 3-BETA-HYDROXYSTEROID DEHYDROGENASE-ISOMERASE REACTIONS. CONVERSION OF ANDROST-4-ENE-3,17-DIONE-4-14C TO 3-BETA-HYDROXYANDROST-4-EN-17-ONE-14C AND 3-BETA-HYDROXYANDROST-5EN-17-ONE-14C. J Biol Chem. 1964 Oct;239:PC3604-6.〕 A typical prohormone is intended to be a precursor of an anabolic steroid like testosterone, which is taken in order to boost the body’s available hormone supply. These precursors are intended to be converted to full, active hormones via an enzymatic process that occurs during metabolism, typically resulting in the addition of whichever atoms happen to be missing from the chemical structure of the compound. Prohormones are used mainly by athletes looking to increase size, strength, endurance, reduce recovery time or add lean body mass. They are most often used for increasing muscle mass or reducing body fat levels. Life extension groups are also increasingly using prohormones as a means of hormone replacement therapy, as an alternative to prescription drug use. Additionally there is a movement to use prohormones of androgens to help offset the damaging effects of environmental estrogens on the body. Chemical endocrine disruptor agents like bisphenol A are becoming recognized as having the ability to skew the androgen to estrogen ratio. This skewed ratio can have many adverse effects on men, including sexual performance, impotence and other testosterone dependent body functions. The use of prohormones has become popular among bodybuilders, since the effects can be similar (though normally much less drastic) to those achieved through the use of synthetic anabolic steroids, including gains in muscular strength and hypertrophy. There are currently many companies manufacturing prohormone products for this purpose. Prohormones have the same side effects as anabolic steroids, and are dependent upon the user as to which side effects one might experience. Some side effects are acne, hair loss, breast tissue enlargement, and prostate swelling; however, these are specific to each type of prohormone, and reports of side effects are usually minimal. The potential for these side effects does exist, but it can be reduced if one uses proper precautionary measures such as post cycle therapy (PCT). Generally, if a person is genetically predisposed to a side effect it will occur (i.e.: if someone has a history of male pattern baldness in the family, it could be assumed that this could be a side effect experienced if prohormones are used) On October 22, 2004, President Bush signed into law the Anabolic Steroid Control Act of 2004 (118 Stat. 1661). The bill was written to become effective in 90 days, which was January 20, 2005. This legislation places both anabolic steroids and some prohormones on a list of controlled substances (a new type of "regulatory control").〔〔Statutory definition of Anabolic steroids: “The term 'anabolic steroid' means any drug or hormonal substance, chemically and pharmacologically related to testosterone (other than estrogens, progestins, corticosteroids and dehydroepiandrosterone)”. The Act also lists substances called prohormones, qualifying them as anabolic steroids, yet these substances were mainly included in the list due to the generalization of the definition of anabolic steroids which makes it currently impossible to synthesize any further substances linked with testosterone for the needs of athlete supplementation.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Prohormone」の詳細全文を読む スポンサード リンク
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