As we see from our discussion with estrogen, in considering the physiological effects of any steroid, we must look at all of its active metabolites, and not just the initial compound. This includes not only estrogenic products, but androgenic metabolites as well. With this in mind, it is important to note that the potency of testosterone is considerably increased in many androgen responsive tissues when it converts todihydrotestosterone. More commonly referred to by the three-letter abbreviation DHT, this hormone is, in fact, measured to be approximately three to four times stronger than testosterone. It is the most potent steroid found naturally in the human body, and important to discuss if we are to understand the full activity of testosterone, as well as other anabolic/androgenic steroids that undergo a similar conversion. Testosterone is converted todihydrotestosterone upon interaction with the 5- alpha reductase enzyme. More specifically, this enzyme removes the C4-5 double-bond of testosterone by the addition of two hydrogen atoms to its structure (hence the name di-hydro testosterone). The removal of this bond is important, as in this case it creates a steroid that binds to the androgen receptor much more avidly than its parent steroid. 5-alpha reductase is present in high amounts in tissues of the prostate, skin, scalp, liver, and various regions of the central nervous system, and as such represents a mechanism for the body to increase the potency of testosterone specifically where strong androgenic action is needed. In these areas of the body little testosterone will actually make its way to the receptor without being converted todihydrotestosterone, making DHT by far the active form of androgen here.
DHT and Androgenic Side Effects
In some regards this local potentiation of testosterone's activity may be unwelcome, as higher androgenic activity in certain tissues may produce a number of undesirable side effects. Acne, for example, is often triggered by dihydrotestosterone activity in the sebaceous glands, and the local formation of dihydrotestosterone in the scalp is typically blamed for triggering male pattern hair loss. You should know that it is a terrible misconception among bodybuilders that dihydrotestosterone is an isolated culprit when it comes to these side effects. All anabolic/androgenic steroids exert their activities, both anabolic and androgenic, through the same cellular androgen receptor. Dihydrotestosterone is no different than any other steroid except that it is a more potent activator of this receptor than most, and can be formed locally in certain androgen-sensitive tissues. All steroids can cause androgenic side effects in direct relation to their affinity for this receptor, and DHT has no known unique ability in this regard.
Benefits of DHT
While a lot of attention is being paid to the negative side effects of the androgen dihydrotestosterone, you should know that there are some known benefits to the strong androgenic activity brought about by this hormone as well. For example, DHT plays an important role in the organization and functioning of the central nervous system. Many neural cells contain active androgen receptors, and it is thought that there may even be a specific importance of dihydrotestosterone in this area of the body. Studies have shown DHT to have a profoundly greater impact in these cells compared to testosterone. More specifically, animal models demonstrated that both testosterone and DHT would result in increased androgen receptor proliferation in neural cells three and seven hours after being administered, however only DHT was able to sustain this increase at the twenty-one hour mark. Although some might contend that this difference is simply due to DHT forming a more stable and lasting complex with the androgen receptor, others suggest that DHT and testosterone might even be affecting neural cells differently, such that the dihydrotestosterone-receptor complex and testosterone-receptor complex might be activating the transcription of different target genes.
The strong interaction between the central nervous system and skeletal muscles, collectively referred to as the neuromuscular system, is of key importance to the athlete. There appears to be little doubt that the ability of the body to adapt to training, and to activate nerve endings in muscle tissue, is reliant on the interactions of the neuromuscular system. Inhibiting the formation of DHT during a testosterone cycle may therefore inadvertently interfere with strength and muscle mass gains. This would explain why bodybuilders commonly report a drop in steroid potency when they add the 5-alpha reductase inhibitor finasteride to a testosterone cycle. Many complain strength and even muscle mass gains slow significantly when this medication is added, which would not make sense if testosterone and androgen receptor activation in muscle tissue were solely responsible for growth. Clearly more is involved, and we cannot look at dihydrotestosterone simply as a side-effect hormone.
Wlliam Llewellyn (2011) - Anabolics