Testosterone is a critical male sex hormone that is responsible for the normal growth and development of the male sex organs and the maintenance of secondary sex characteristics, such as the growth and maturation of male sex organs, the development of male hair distribution, vocal cord thickening, and alterations in body musculature and fat distribution. Male hypogonadism, resulting from insufficient testosterone secretion, has two main etiologies: primary hypogonadism is caused by defects in the gonads, whereas secondary hypogonadism is the failure of the hypothalamus (or pituitary) to produce sufficient gonadotropins (FSH and LH).
In the circulation, testosterone undecanoate is cleaved by endogenous non-specific esterases to release testosterone, the active component of the compound. The undecanoate side chain is pharmacologically inactive. Testosterone can be further converted by 5α reductase to its more biologically active form, dihydrotestosterone (DHT). The actions of testosterone and DHT are mediated via androgen receptor, which is widely expressed in many tissues, including the bone, muscle, prostate, and adipose tissue. Testosterone binds to androgen receptors with high affinity and regulates target gene transcription involved in the normal growth and development of the male sex organs and the maintenance of secondary sex characteristics.Testosterone can cause improved sexual function, increased lean body mass, bone density, erythropoiesis, prostate size, and changes in lipid profiles.
