What Does Testosterone Do: Simple Overview
When free in the blood stream, testosterone can interact with various cells in the body. These include skeletal muscle cells and fat cells as well as skin, scalp, kidney, prostate, bone and brain cells. In the case of muscle cells, testosterone promotes an increase in the synthesis of two muscle-building proteins. In the case of fat cells, it promotes fat mobilization. It is no surprise that testosterone replacement therapy (TRT) has been shown to increase muscle and decrease fat.
In the case of kidney cells, testosterone promotes red blood cell production. Too much of an increase in red blood cell production may lead to too high red blood cell concentrations, one of the potential side effects of testosterone therapy. It also promotes the secretion of oils in the skin and the production of body and facial hair during puberty and may help initiate male-pattern hair loss later in life (largely based on a genetic predisposition). Both bone and brain cells also interact with a converted form of testosterone known as estradiol.
What Does Testosterone Do: Detailed Explanation
Testosterone elicits changes only in cells that possess androgen receptors. These cells include skeletal muscle cells and fat cells as well as skin, scalp, kidney, prostate, bone and brain cells. As both free and testosterone bound to albumin flow through the bloodstream, it interacts with a cellular target’s androgen receptor to form a new receptor complex located in the cytosol. This process can be likened to a lock and key mechanism. The cell’s receptor is the “lock” and the hormone, in this case testosterone, is the “key”. This complex then migrates to the cell’s nucleus. Then, it attaches to the cell’s DNA and promotes the synthesis of a specific gene. One this process completes, the complex will be released, and the receptor and testosterone molecule will dissociate. At this time, the free testosterone can migrate back into the cytosol for further activity or back into the blood stream. Any testosterone bound to sex hormone binding globulin is inactive.
As mentioned above, in the case of muscle cells, testosterone promotes an increase in the synthesis of two muscle-building proteins (actin and myosin). In the case of fat cells, it promotes lipolytic capacity (fat mobilization and breakdown). In the case of kidney cells, it promotes erythropoiesis (red blood cell production). Too much of an increase may lead to one potential side effect of TRT (too high red blood cell concentrations).
Testosterone can also be reduced by 5-alpha-reductase to 5-alpha-dihydrotestosterone, simply known as dihydrotestosterone (DHT). DHT binds to the same androgen receptor even more strongly than testosterone. Its androgenic potency is about five times that of testosterone. DHT primarily elicits bodily change in the skin, scalp, and prostate cells. Specifically, DHT initiates the secretion of oils in the skin. It also promotes the production of body and facial hair during puberty and may help initiate male-pattern hair loss later in life (largely based on a genetic predisposition). Importantly, DHT also interacts with prostate cells. Thus, testosterone replacement therapy is controversial for patients with known prostate cancer. Fortunately, most studies agree that TRT does not induce a development of malignant prostate cells that were not previously present.1-5
Lastly, testosterone can also be converted into estradiol, the principle female sex hormone. Estradiol elicits changes in various regions of the male body. These regions include fat, liver, gonadal, central nervous system, and skeletal muscle. In the context of the average healthy male, the amount of estrogen present does not significantly change body composition. TRT dosages that do not exceed normal levels tend not lead to any feminizing effects. However, larger amounts of estrogen may lead to water retention and breast enlargement. Larger amounts of estrogen may be due to TRT dosages that are too high or other underlying issues. Taking anastrozole (brand name Arimidex) may help control high estradiol levels.
Updated: April 18, 2015
1. Rosenfield RL. Role of androgens in growth and development of the fetus, child, and adolescent. Adv. Pediatr. 19 (1972) 172-213.
2. Carter HB, Pearson JD, Metter EJ, et al. Longitudinal evaluation of serum androgen levels in men with and without prostate cancer. Prostate. Jul 1995; 27 (1): 25-31.
3. Slater S, Oliver RT. Testosterone: its role in development of prostate cancer and potential risk from use as hormone replacement therapy. Drugs Aging. Dec 2000; 17 (6): 431-439.
4. Heikkilä R, Aho K, Heliövaara M, et al. Serum T and sex hormone-binding globulin concentrations and the risk of prostate carcinoma: a longitudinal study. Cancer. Jul 1999; 86 (2): 312-315.
5. Hsing AW. Hormones and prostate cancer: what’s next? Epidemiol Rev. 2001; 23 (1): 42-58.