Males
The principal androgen (male sex hormone) is testosterone. This steroid is manufactured by the interstitial (Leydig) cells of the testes. Secretion of testosterone increases sharply at puberty and is responsible for the development of the so-called secondary sexual characteristics (e.g., beard) of men.
Testosterone is also essential for the production of sperm.
Production of testosterone is controlled by the release of luteinizing hormone (LH) from the anterior lobe of the pituitary gland, which is in turn controlled by the release of GnRH from the hypothalamus. LH is also called interstitial cell stimulating hormone (ICSH).
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Hypothalamus |
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GnRH |
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Pituitary |
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LH |
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Testes |
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Testosterone |
The level of testosterone is under negative-feedback control: a rising level of testosterone suppresses the release of GnRH from the hypothalamus. This is exactly parallel to the control of estrogen secretion in females.
Genetic abnormalities of gonadal function.
Many things can go wrong with sexual development in both males and females; fortunately rarely. Let's look only at a few that clearly result from the inheritance of single-gene mutations.
- Inherited mutations in both copies of the gene encoding the GnRH receptor result in failure to develop at puberty.
- Mutations in the gene encoding the LH receptor prevent normal sexual development in both sexes.
- Mutations in the gene encoding the FSH receptor block development of the gonads in both males and females.
- Mutations in any of the genes encoding the enzymes for synthesis and metabolism of testosterone interfere with normal sexual function in males.
- A similar spectrum of disorders in males can be caused by mutations in the genes encoding the androgen receptor.
Males need estrogen, too!
In 1994, a man was described who was homozygous for a mutation in the gene encoding the estrogen receptor. A single nonsense mutation had converted a codon (CGA) for arginine early in the protein into a STOP codon (TGA). Thus no complete estrogen receptor could be synthesized.
This man was extra tall, had osteoporosis and "knock-knees", but was otherwise well. His genetic defect confirms the important role that estrogen has in both sexes for normal bone development.
It is not known whether this man (or any of the few other men who have been found with the same disorder) is fertile or not. However, an article in the 4 December 1997 issue of Nature reports that male mice whose estrogen receptor gene has been "knocked out" are sterile.
Anabolic steroids
A number of synthetic androgens are used for therapeutic purposes. Unfortunately, these drugs also promote an increase in body weight and muscle strength. This has made them increasingly popular with athletes: weight lifters, cyclists, professional football players, etc.
Often these athletes take doses 100 time greater than those used in standard therapy. Such illicit use carries dangers (besides being banned from an event because of a positive drug test): acne, a decrease in libido, testicle size, and sperm counts to name a few.
