L23 (T1): Endocrine aspects of male hypogonadism

Understanding Testosterone and Male Hypogonadism

• Testosterone is a steroid hormone secreted in both men and women from the testes, ovary, and adrenal glands, with normal young men producing about 7 mg each day, primarily from the testes.
• In blood, testosterone is predominantly bound to plasma proteins, with less than 5% derived from adrenal secretions and only about 2% present as free hormone.
• The synthesis of androgens involves the conversion of cholesterol to various intermediates, ultimately leading to the production of testosterone and its conversion to dihydrotestosterone (DHT) and estradiol.
• Testosterone, like other steroid hormones, penetrates target cells to stimulate growth and function, with androgen target cells generally converting testosterone to DHT before binding to the androgen receptor.
• Male hypogonadism is defined as the failure of the testes to produce adequate testosterone, leading to a decrease in sperm production or testosterone production, and can be caused by primary (testicular) or secondary (hypothalamic or pituitary) factors.
• Primary hypogonadism is characterized by low testosterone and elevated serum LH and/or FSH, while secondary hypogonadism features low testosterone and normal or low serum LH and/or FSH.
• Causes of male hypogonadism include genetic disorders, infections, trauma, tumors, medications, and systemic illnesses, with clinical features ranging from incomplete sexual development to decreased libido and infertility.
• Screening for male hypogonadism is suggested in conditions such as pituitary mass, medication use affecting testosterone production, HIV-associated weight loss, and infertility, with a focus on history, physical examination, and investigations including hormone levels, semen analysis, and imaging.
• Key investigations for male hypogonadism include serum testosterone, LH/FSH, SHBG, liver function tests, semen analysis, karyotyping, pituitary function testing, and DEXA scan for bone density.
• Guidelines on screening for male hypogonadism recommend initial morning total testosterone levels, with consideration of age-dependent normal ranges and exclusion of reversible causes before diagnosis and follow-up.
• The text provides a comprehensive overview of the synthesis, action, regulation, and clinical aspects of testosterone, as well as the diagnosis and management of male hypogonadism.
• The link provided offers further resources on testosterone testing and related information for clinical use.

Understanding Testosterone and its Effects

• The testicle contains sertoli cells that produce anti-mullerian hormone (AMH) and inhibit follicle-stimulating hormone (FSH), and leydig cells that produce testosterone.
• Testosterone synthesis begins with cholesterol, which is converted to pregnenolone, then to progesterone and DHEA, eventually leading to testosterone production.
• Testosterone can be converted to dihydrotestosterone (DHT) or aromatized to estradiol, the latter being a concern for those taking excess androgens.
• The hypothalamic-pituitary-testicular axis involves the pulsatile secretion of luteinizing hormone (LH) and FSH, which stimulate testosterone and spermatogenesis production.
• Excess testosterone leads to negative feedback regulation, reducing the production of LH and FSH to prevent further testosterone increase.
• Testosterone can enter cells and be converted to DHT, which has about five times more potency than testosterone, affecting specific induced proteins and resulting in various effects.
• Testosterone has numerous effects, including increased beard growth, prostate growth, laryngeal development, penis size, sperm production, muscle mass, and cholesterol levels.
• Testosterone increases the risk of myocardial infarction due to its impact on cholesterol levels, and it affects sex drive, external genitalia production, and the development of reproductive organs in the fetus.
• Low testosterone levels can lead to depression, fatigue, memory loss, and an increased risk of Alzheimer's disease.
• The effects of testosterone are influenced by its conversion to DHT or estradiol, with potential synergistic or antagonistic effects.
• Testosterone has a wide range of effects on the human body, impacting physical, reproductive, and psychological aspects.
• Understanding the synthesis and effects of testosterone is crucial for comprehending its role in the body and in medical conditions related to hormonal imbalance.

Test your knowledge of testosterone and male hypogonadism with this informative quiz. Explore the synthesis, action, regulation, and clinical aspects of testosterone, and learn about the diagnosis and management of male hypogonadism. Test your understanding of key investigations and guidelines for screening, and enhance your knowledge of this important hormone and its implications for men's health.