Androsterone

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Androsterone is an endogenous steroid hormone and neurosteroid. It is a weak androgen—about one-seventh as potent as testosterone—and it is a metabolite of testosterone and dihydrotestosterone (DHT). It can also be converted back into DHT, making it a metabolic intermediate in androgen synthesis.

What it does and how it’s made
- In the body, testosterone and DHT are transformed step by step to form androsterone. Enzymes such as 5α-reductase, 5β-reductase, 3α- and 3β-hydroxysteroid dehydrogenase, and 17β-hydroxysteroid dehydrogenase are involved in these conversions.
- The 3α-hydroxy form is the main active version, while the 3β form is epiandrosterone. There are also 5β-epimers like etiocholanolone.
- Androsterone can be further modified by sulfate or glucuronide groups to be excreted in urine.

Brain effects and potential roles
- Androsterone acts as a positive allosteric modulator of the GABAA receptor, giving it nerve-calming, anticonvulsant properties.
- The unnatural (synthetic) version of androsterone can be more potent in these respects than the natural form.
- It may influence brain function and behavior when present in the brain.

Backdoor pathway and fetal development
- Recent research highlights androsterone as a significant player in what’s called the “backdoor” pathway to DHT, which helps masculinize the external genitalia in mammals, including humans.
- In male fetuses, backdoor androgen production mainly occurs in the liver and adrenal glands, with the placenta providing progesterone as a substrate. This pathway helps explain some developmental effects when normal androgen pathways are disrupted.
- The female fetus has very low levels of DHT and backdoor intermediates.

Occurrence and odor
- Androsterone is found in human axilla (underarms), skin, and urine, and can be secreted by sebaceous glands.
- It has a musky odor, similar to other related steroids, and this odor can influence behavior in some contexts.

Natural sources and discovery
- It is produced in the body as a metabolite of testosterone and DHT, and can also be found in foods and plants such as pine pollen, celery, and truffles.
- Androsterone was first isolated in 1931 by Butenandt and Tscherning from a large batch of distilled male urine, from which a tiny amount was recovered.