Testosterone is a 19-carbon, anabolic-androgenic steroid hormone which is produced in all vertebrates. The production of testosterone is regulated by the hypothalamus – which is located within the brain near the pituitary gland. Testosterone is the primary male sex hormone and is predominantly secreted in the testicles of males (95%) and a small percentage in the adrenal glands above the kidneys (2%) – with normal male values ranging from 300 – 1000 ng/dL. Women also produce testosterone in small quantities 15 – 70 ng/dL, by the ovaries and is involved in the maintenance, repair and growth of female reproductive tissue.
The process in which males produce testosterone starts with the hypothalamus, once the hypothalamus detects the body needs more testosterone it produces and secretes a hormone called gonadotropin (GnRH) – also known as luliberin and luteinzing-hormone-releasing hormone (LHrH).
Gonadotropin is responsible for stimulating the pituitary gland. Once produced and secreted, gonadotropin is transported to the pituitary gland through the blood stream – once detected by the pituitary gland it stimulates the production of luteinising hormone (LH) and follicle stimulating hormone (FSH). These hormones act synergistically and once released into the blood stream they make their way to the testicles, where action is taken to initiate and maintain reproductive functions.
Follicle stimulating hormone (FHS): In men FHS stimulates the production of sperm (spermatogenesis). Once at the testicles, FHS stimulates spermatocytes to undertake the first division of meiosis to form secondary spermatocytes.
Luteinising hormone (LH): Is crucial for regulating function of the testicles by stimulating leydig cells to produce testosterone. Leydig cells also need a constant and adequate supply of cholesterol for testosterone production.
Once testosterone is produced, it will act locally to sustain sperm production and play a key role in the maintenance, repair and growth of male reproductive tissue. Testosterone is also sent through the blood stream and exerted all around the body to generate male characteristics. Testosterone directly impacts muscle growth – once bound to receptors on the muscle cells surface it amplifies the biochemical signals in skeletal muscle tissue and results in protein synthesis.
The two most important hormones in relation to building muscle are testosterone and growth hormone. Testosterone increases levels of growth hormone which the body would normal release in response to a workout. Like testosterone, growth hormone results in increased muscle mass by increasing protein synthesis.