Testosterone is the most important sex hormone in men, responsible for the development of male physical characteristics. It is mainly produced in the testicles, with a small percentage also produced in the adrenal glands. Testosterone binds to plasma proteins, such as globulin and albumin, and is aromatized to 17β-estradiol, which has essential functions in bone development. Low testosterone levels can delay puberty and have a negative effect on muscle mass, bone density, body fat, libido, and mood.
It is also used to treat medical conditions such as metastatic breast cancer, delayed puberty, hypogonadotropic hypogonadism (congenital or acquired), and primary hypogonadism. Testosterone binds to the androgen receptor (AR) and regulates gene transcription through the classical genomic pathway. Δ-9-tetrahydrocannabinol (THC), the active ingredient in cannabis, causes a decrease in the release of FSH and LH, resulting in a decrease in serum testosterone levels in both experimental animals and humans. Testosterone is also responsible for primary sexual development, including testicular decline, spermatogenesis, penis and testicle enlargement, and increased libido.
Dehydroepiandrosterone (DHEA) is another important hormone that differs from testosterone. Some studies have shown that there is no increased risk of prostate cancer with testosterone replacement therapy, but it is still an ongoing research topic. If you know your total testosterone reading from a previous blood test, you can enter the results to see if your testosterone levels are normal. Testosterone levels tend to decline with age; because of this, men tend to experience a decrease in testicular size, a decrease in libido, a decrease in bone density, a decrease in muscle mass, an increase in fat production and a decrease in erythropoiesis, leading to a possible anemia. More than 95% of endogenous testosterone is produced in the testicles and 6 to 7 mg are secreted every day.
Testosterone is produced by Leydig cells in the interstitial compartment in response to the binding of LH to its specific Leydig cell membrane receptor. Since testosterone cannot be stored in Leydig cells, it must be continuously produced again.