Testostrone

Testosterone is a naturally occurring hormone called an androgen. Testosterone is produced in the testes in men, and small amounts are produced by the ovaries and adrenal cortex in women. Testosterone is used in men and boys to treat conditions due to androgen deficiency, such as lack of natural testosterone, delayed puberty, and impotence. Testosterone may be used by women to treat some types of cancer.

Take this medication by mouth as directed, usually once or twice a day. This is best taken after a meal to reduce stomach upset. Swallow capsules whole. Try to take this medication at the same time each day so you get in the habit of taking it. Do not increase your dose or take this more often than directed. It will have no greater benefits but the risk of side effects will be increased.

The effects of testosterone in humans and other vertebrates occur by way of two main mechanisms: by activation of the androgen receptor (directly or as DHT), and by conversion to estradiol and activation of certain estrogen receptors.

Free testosterone (T) is transported into the cytoplasm of target tissue cells, where it can bind to the androgen receptor, or can be reduced to 5alpha-dihydrotestosterone (DHT) by the cytoplasmic enzyme 5alpha-reductase. DHT binds to the same androgen receptor even more strongly than T, so that its androgenic potency is about 2.5 times that of T. The T-receptor or DHT-receptor complex undergoes a structural change that allows it to move into the cell nucleus and bind directly to specific nucleotide sequences of the chromosomal DNA. The areas of binding are called hormone response elements (HREs), and influence transcriptional activity of certain genes, producing the androgen effects.

Androgen receptors occur in many different vertebrate body system tissues, and both males and females respond similarly to similar levels. Greatly differing amounts of testosterone prenatally, at puberty, and throughout life account for a large share of biological differences between males and females.

The bones and the brain are two important tissues in humans where the primary effect of testosterone is by way of aromatization to estradiol. In the bones, estradiol accelerates maturation of cartilage into bone, leading to closure of the epiphyses and conclusion of growth. In the central nervous system, testosterone is aromatized to estradiol. Estradiol rather than testosterone serves as the most important feedback signal to the hypothalamus (especially affecting LH secretion). In many mammals, prenatal or perinatal "masculinization" of the sexually dimorphic areas of the brain by estradiol derived from testosterone programs later male sexual behavior.