Andro; andros; 4-Androstenedione. 17 ketotestosterone; 4-androsten-3,17-dione
Androstenedione is described as a ‘pro-hormone’ because it has few effects itself. Instead, it is important because of the ability of different parts of the body to convert it into the hormones, testosterone and oestrogen, which exert many effects on the body.
In females, the outer part of the adrenal glands (known as the cortex) and the ovaries release androstenedione into the bloodstream where it is converted to provide around half of all testosterone and almost all of the body's oestrone, a form of oestrogen. Although the testes produce large amounts of androstenedione in males, they secrete little of this into the blood and, instead, rapidly convert it into testosterone within the testes. The adrenal glands also produce androstenedione in men, but this contribution is swamped by the testes' overwhelming production of the other androgenic hormone, testosterone.
Due to its secretion from a number of different glands and its often rapid conversion to other hormones, the control of androstenedione within the body is very complex. However, two key parts of the brain (the hypothalamus and pituitary gland) are known to be important in the control of androstenedione secretion from the testes, ovaries and adrenal cortex. The release of androstenedione by the adrenal cortex is thought to be related to the pituitary gland’s secretion of a specialised hormone, adrenocorticotropic hormone. Precisely how adrenocorticotropic hormone and other hormones control the adrenal gland’s production of androstenedione is, however, unclear. The testes and ovaries are stimulated to release androstenedione by luteinising hormone and follicle stimulating hormone. These are released from the anterior pituitary gland in response to a hormone signal from the hypothalamus.
The effects of too much androstenedione are likely to result from its conversion in the body to oestrogen or testosterone.
In men, too much androstenedione may lead to an imbalance in oestrogen and testosterone production, leading to changes such as breast development. Depending on the cause of the excess androstenedione, other changes, such as the testes becoming smaller, might also occur.
Although androstenedione is often abused by bodybuilders in an effort to build muscle bulk, a small number of studies have suggested that its long-term use may actually decrease muscle strength. The precise consequences of having too much androstenendione are, therefore, still unclear.
Boys with too little androstenedione may fail to develop the sexual characteristics associated with puberty, including pubic and body hair, growth of the sexual organs and deepening of the voice. Similarly, girls may fail to start their periods and may not undergo many of the changes usually seen in puberty. In addition, if a male foetus has too little androstenedione, he may be born with abnormal genitalia. Too little androstenedione in later life would cause the same changes for both men and women as too little testosterone and oestrogen.
Last reviewed: Jan 2017