Testosterone

Testosterone

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Testosterone ball

Human Steroidogenesis

Hypothalamic–pituitary–testicular axis

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Dimeric sex-hormone-binding-globulin with its testosterone ligands

Two methods for determining concentration of bioavailable testosterone

Nobel Prize winner, Leopold Ruzicka of Ciba, a pharmaceutical industry giant that synthesized testosterone.

Testosterone_structure.jpg Chemical structure of Testosterone

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Testosterone is the primary male sex hormone and is classified as an anabolic steroid. This hormone plays a pivotal role in the maturation of male reproductive tissues, such as the testes and prostate. Additionally, it stimulates the emergence of secondary sexual characteristics, including the enhancement of muscle and bone mass, as well as fostering the growth of body hair.

Role in the Body

Beyond its function in fostering male sexual characteristics, testosterone contributes to overall health and well-being, aiding in the prevention of osteoporosis. A deficiency in testosterone levels in males can usher in health issues like frailty and bone loss.

Structure and Synthesis

Testosterone is an androstane class steroid, characterized by keto and hydroxyl groups situated at the three and seventeen positions, respectively. It undergoes biosynthesis from cholesterol and is subsequently converted in the liver to inactive derivatives. The hormone primarily exerts its influence by binding to and thus activating the androgen receptor.

Production and Regulation

In humans and a majority of vertebrates, testosterone is chiefly produced by the male testicles and to a minor extent by female ovaries. In adult males, testosterone levels average out to be approximately 7 to 8 times higher than in adult females. This disparity is attributed to the more pronounced metabolism of testosterone in males, with daily production being around 20 times more than in females. It is noteworthy that females demonstrate a heightened sensitivity to the hormone.

Medical Uses

Testosterone finds utility not only as a natural hormone but is also employed medicinally for diverse purposes. It aids in the treatment of men with low testosterone levels, serves as a hormone therapy for transgender men, and is used in treating breast cancer in women. With the natural decline of testosterone in aging males, it is sometimes administered to counterbalance this decrease. However, its illicit use to enhance physique and performance, especially among athletes, is a concern.

Biological Effects

Androgens, which include testosterone, primarily promote protein synthesis, thus fostering the growth of tissues having androgen receptors. Testosterone’s influence can be broadly categorized into virilizing and anabolic effects.

Anabolic Effects

Testosterone boosts the growth of muscle mass and strength, augments bone density and strength, and stimulates linear growth along with bone maturation.

Androgenic Effects

Its androgenic impact is evident in the development of sex organs, especially during fetal development, deepening of voice post-puberty, and growth of facial and axillary hair, which are recognized as male secondary sexual characteristics.

Other Effects

Testosterone is instrumental for normal sperm development. It activates genes in Sertoli cells, propelling differentiation of spermatogonia. The hormone also controls the acute HPA (hypothalamic–pituitary–adrenal axis) response under dominance challenge scenarios. Androgens, inclusive of testosterone, stimulate muscle growth. Testosterone also plays a role in managing thromboxane A2 receptor populations on megakaryocytes and platelets, impacting platelet aggregation.

While the effects of testosterone are more prominently observed in males, they remain significant for both genders. Some effects might recede as testosterone levels potentially decrease in later adult years.

Health Implications

Contrary to common belief, testosterone does not escalate the risk of developing prostate cancer. However, for those undergoing testosterone deprivation therapy, any surge in testosterone levels beyond the castrate mark might accelerate the spread of existing prostate cancer.

The role of testosterone in cardiovascular health remains contentious. Nonetheless, sustaining standard testosterone levels in elderly men has shown to enhance various metrics believed to curtail cardiovascular disease risk.

High androgen concentrations can lead to menstrual cycle irregularities in both clinical populations and healthy women.

Sexual Arousal

When testosterone and endorphins in ejaculated semen come in contact with the cervical wall post intercourse, females experience an elevation in testosterone, endorphin, and oxytocin levels. Males post-orgasm experience heightened endorphin levels and a marked rise in oxytocin. This creates a favorable physiological environment for conception and fosters feelings of love, desire, and paternal care in males.

Testosterone levels display a nyctohemeral rhythm, peaking early daily irrespective of sexual activity. Positive correlations exist between pleasurable orgasm experiences in women and testosterone levels, with relaxation being a significant perception. No such correlations exist between testosterone and men's perceptions of their orgasm experience or between higher testosterone levels and increased sexual assertiveness in either gender.

Testosterone Therapy

Testosterone therapy, often referred to as testosterone replacement therapy (TRT), is a widely recognized treatment for men with diminished testosterone levels. It can be delivered through injections, patches, gels, or pellets. TRT is prescribed primarily to treat hypogonadism, a condition where the body fails to produce adequate testosterone due to testicular or pituitary gland issues.

The therapy offers multiple benefits, including enhanced energy, uplifted mood, augmented muscle mass, and improved sexual functionality. However, potential risks are also associated, like increased chances of blood clots, heart attacks, and prostate cancer.

Testosterone therapy has also found utility in transgender hormone therapy for transgender men and, in certain scenarios, to treat breast cancer in women.

Illicit use of testosterone, especially in the domain of sports and bodybuilding, poses risks, including liver damage, cardiovascular diseases, reduced fertility, and mood disorders.

Testosterone and Aging

Testosterone levels naturally wane with age in both genders, initiating around the age of 30. This gradual reduction, occurring at an estimated rate of 1% annually, is linked with age-associated health concerns in males, including muscle mass reduction, increased fat accumulation, decreased bone density, and cognitive decline.

While testosterone replacement therapy is an option for older men, its risks and benefits remain a topic of discussion. Individual health profiles should dictate the decision to undergo therapy.

See Also

• Anabolic steroid
• Androgen receptor
• Hormone therapy
• Prostate cancer

References

Testosterone Resources
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