Endogenous androgens, mainly testosterone secreted by the testes, and their main metabolite, dihydrotestosterone, are responsible for the development of external and internal genital organs and for the development and preservation of secondary sexual characteristics (stimulating hair growth, coarsening of the voice), libido; for the overall effect on protein anabolism; for the development of skeletal muscles and the distribution of subcutaneous fat; for a decrease in urinary excretion of nitrogen, sodium, potassium, chlorides, phosphates and water. Testosterone does not cause the development of testicles: it reduces the pituitary secretion of gonadotropins.
The effects of testosterone on certain target organs appear after the peripheral conversion of testosterone to estradiol, which then binds to estrogen receptors in the nuclei of target organ cells (such as the pituitary gland, adipose tissue, brain, bones, etc.).