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Androstenedione, or 4-androstenedione (abbreviated as A4 or Δ4-dione), also known as androst-4-ene-3,17-dione, is an endogenous weak androgen steroid hormone and intermediate in the biosynthesis of estrone and of testosterone from dehydroepiandrosterone (DHEA). It is closely related to androstenediol (androst-5-ene-3β,17β-diol).
Androstenedione has been found to possess some activity, similarly to other DHEA metabolites. However, in contrast to androstenediol, its affinity for the estrogen receptors is very low, with less than 0.01% of the affinity of estradiol for both the ERα and ERβ.
Androstenedione can be biosynthesized in one of two ways. The primary pathway involves conversion of 17α-hydroxypregnenolone to DHEA by way of 17,20-lyase, with subsequent conversion of DHEA to androstenedione via the enzyme 3β-hydroxysteroid dehydrogenase. The secondary pathway involves conversion of 17α-hydroxyprogesterone, most often a precursor to cortisol, to androstenedione directly by way of 17,20-lyase. Thus, 17,20-lyase is required for the synthesis of androstenedione, whether immediately or one step removed.
Androstenedione is produced in the and the . The production of adrenal androstenedione is governed by adrenocorticotrophic hormone (ACTH), whereas production of gonadal androstenedione is under control by the . In premenopausal women, the adrenal glands and ovary each produce about half of the total androstenedione (about 3 mg/day). After menopause, androstenedione production is about halved, due primarily to the reduction of the steroid secreted by the ovary. Nevertheless, androstenedione is the principal steroid produced by the postmenopausal ovary.
Some androstenedione is also secreted into the blood plasma, and may be converted in peripheral tissues to testosterone and estrogens.
Androstanedione is a 5α-reduced metabolite of 4-androstenedione which serves as an intermediate in the biosynthesis of the androgen and neurosteroid androsterone.
Androstenedione also has a variety of metabolites in different species. In cattle, androstenedione is converted into oestradiol-17 and epitestosterone. In sheep, the molecule is transformed into the 17-epimer. Androstenedione is converted into different metabolites in invertebrates. As is the case for Marisa cornuarietis, freshwater ramshorn snail, where androstenedione is converted into 5α-dihydrotestosterone (DHT) and testosterone (T) in male and into 5α-dihydroandrostenedione (DHA) in females.
In premature infants, serum androstenedione levels hover between 80 and 446 ng/dL. In full-term newborns, levels range from 20 to 290 ng/dL, and between 1 month and 1 year old, serum levels typically stay at less than 69 ng/dL.
Serum levels of androstenedione greater than or equal to 500 ng/dL may indicate the presence of an adrenal or gonadal tumor.
A 2006 review paper summarized several studies that examined the effect of androstenedione on strength training. At dosages of 50 mg or 100 mg per day, androstenedione had no effect on muscle strength or size, or on body fat levels. One study used a daily dosage of 300 mg of androstenedione combined with several other supplements, and also found no increase in strength when compared to a control group that did not take the supplements.
The review authors speculate that sufficiently high doses may indeed lead to increased muscle size and strength. However, due to the federal ban on androstenedione supplements, it is difficult to carry out new research on its effects. The review authors conclude that individuals should not use androstenedione supplements due to the lack of evidence of beneficial effects, the wide variation in individual responses to the supplement, and the risk of unknown side effects. Side effects for women may include the development of male characteristics, clitoromegaly, voice deepening, hirsutism, abnormal menstrual cycles and abnormal bleeding, blood clots, and metabolic disruption based on a study following 10 healthy females administering 100 mg androstenedione.
Barry R. McCaffrey, in his capacity as director of the White House Office of National Drug Control Policy from 1996 to 2001, determined that androstenedione could not be classified as an anabolic steroid because there is no proof that it promotes muscle growth.
On March 12, 2004, the Anabolic Steroid Control Act of 2004 was introduced into the United States Senate. It amended the Controlled Substances Act to place both and on a list of controlled substances, making possession of the banned substances a federal crime. The law took effect on January 20, 2005. However, androstenedione was legally defined as an anabolic steroid, even though there is scant evidence that androstenedione itself is anabolic in nature. On April 11, 2004, the United States Food and Drug Administration banned the sale of androstenedione, citing that the drug poses significant health risks commonly associated with steroids. Androstenedione is currently banned by the U.S. military.
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