Why Does Testosterone Decrease | The Truth About Testosterone
HPTA = Hypothalamic Pituitary Gonadal Axis
This axis produces circulating steroids necessary for male sexual function, fertility, and development.
Prostate and penis are steroid sensitive organs impacted by the regulation of the HPTA.
This reproductive axis consists of three parts:
- Hypothalamus – produces GnRH (gonadotropin-releasing hormone)
- Pituitary Gland – GnRH sent to the pituitary gland where it stimulates the synthesis and release of gonadotropic hormones LH and FSH.
- Testis – Gonads carry LH to the testis where they encourage testosterone production through the testicular Leydig cells
- Conversion of cholesterol produces testosterone
- FSH is crucial for spermatogenesis
Dihydrotestosterone (DHT) is the activated 2% of testosterone is free or unbound, with the remainder bound to SHBG (sex hormone-binding globulin), albumin- and cortisol-binding globulin. Bioavailable testosterone is the testosterone that will not attach to SHBG. Testosterone and DHT act on organs.
- Causes development of secondary sexual characteristics
- Inhibit secretion of LH and FSH by the pituitary gland, thus stops further testosterone production = negative feedback loop.
- There exist androgen receptors in the pituitary and the
hypothalamic neurons that bind to testosterone and signal to stop GnRH release
Homeostasis maintained through this loop – once testosterone stops production, this inhibited secretion stops and GnRH again causes LH and FSH release to produce further testosterone. As men age, they undergo hormonal level changes:
- Testosterone decrease
- LH and FSH increase
- Other hormones that decrease: T3, insulin, growth hormone/insulin-like growth factor 1, stimulating thyroid hormone
- Also an increase in SHBG
- Dihydrotestosterone levels are unchanged
- Estrogen levels unchanged
As men age, the decrease in testosterone paired with the increase in SHBG leads to a decline in free, or bioavailable, testosterone. These hormonal changes start in the 30s and are well established by the 50s.
The Purpose of Testosterone injections Therapy:
- Improve Motivation and Memory Loss
- Increase Sex Drive & Desire
- Improve Depression and Energy
- Improve Cholesterol and Osteoporosis
- Decrease Erectile Dysfunction
- Increase Muscle Mass and Better Sleep
- Improve Wounds healing & Illness
- Improve Thyroid Dysfunction