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Male Hormones

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Topic updated on 12/16/16 11:17am

Androgens
  • Sources of androgens
    • males
      • testes are a major source of androgens
      • adrenal cortex is a minor source of androgens
    • females
      • adrenal cortex is a major source of androgens
  • Androgen biosynthesis
    • adrenal cortex
      • in adrenal cortex, zona reticularis synthesizes and secretes adrenal androgens via a biosynthetic pathway that begins with cholesterol
        • androstenedione and dehydroepiandrosterone (DHEA)
    • testes
      • Leydig cells of testes synthesize and secrete testosterone via a biosynthetic pathway that begins with cholesterol
        • Leydig cells express 17β-hydroxysteroid dehydrogenase
          • catalyzes conversion of androstenedione to testosterone
        • Leydig cells lack 21β-hydroxylase and 11β-hydroxylase
          • testes cannot synthesize and secrete glucocorticoids and mineralocorticoids
      • Leydig cells of testis may also synthesize and secrete dihydrotestosterone (DHT)
        • Leydig cells express 5α-reductase
          • catalyzes conversion of testosterone to DHT
    • Androgenic target tissues
      • in some androgenic target tissues, DHT is an active androgen
        • androgenic target tissues express 5α-reductase
          • catalyzes conversion of testosterone to DHT
  • Androgen potency
    • DHT > testosterone > androstenedione
  • Androgen function
    • actions mediated by testosterone
      • fetal differentiation of internal male genitalia
        • epididymis, vas deferens, and seminal vesicles
      • pubertal growth spurt
        • growth of penis and seminal vesicles
        • deepening of voice
      • increased muscle mass
      • cessation of pubertal growth spurt
        • epiphyseal plate closure
          • mediated by estrogen
            • testosterone → estrogen via aromatase
              • in testes, Sertoli cells express aromatase enzyme
                • catalyzes conversion of testosterone to estrogen
                • additionally, adipose tissue expresses aromatase enzyme
    • actions mediated by DHT
      • fetal differentiation of external male genitalia
        • penis, scrotum, and prostate
      • male hair pattern and male pattern baldness
      • sebaceous gland activity
      • growth of prostate
  • 5α-reductase inhibitors
    • e.g., finasteride
    • inhibit conversion of testosterone to DHT
    • DHT mediates male hair pattern and growth of prostate
      • 5α-reductase inhibitors may be used in treatment of benign prostatic hyperplasia (BPH) and hair loss in males
  • Exogenous testosterone
    • exogenous testosterone inhibits hypothalamic-pituitary-gonadal axis
      • decreases testosterone levels in testes
        • decreases size of testes
        • causes azoospermia


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