Predominately secreted by the testes, with a very small amount secreted by the adrenal gland.
Testosterone is the most significant anabolic hormone produced by the human body. Testosterone is fundamentally responsible for the development of male sexual characteristics in males. It also plays a dominant role in the growth of lean muscle tissue, sustain energy levels and immune function. Testosterone increases bone density and is shown to increase strength. It is also vital for protein synthesis as it is a primary growth factor. Testosterone amplifies the biochemical signals within muscles through the process of binding to receptors on the surface of muscle cells. This results in protein synthesis and lean muscle tissue growth.
Testosterone assists in increasing growth hormone (GH) levels, additionally enhancing protein synthesis.
Luteinizing hormone (LH) stimulates testosterone synthesis from Leydig cells in the testes.
Follicle stimulating hormone (FSH) stimulates the production of androgen-binding protein from Sertoli cells of the testes.
Insulin sensitivity is also linked to the changes in the testosterone-cortisol balance.