Dihydrotestosterone (DHT) is the primary androgen acting in the epididymis - DHT responsible for sperm motility but not sperm count?
https://www.ncbi.nlm.nih.gov/pubmed/17003279
*Finisteride*
Supplemental testosterone seems to promote muscle growth, even if given alongside finisteride, a DHT inhibitor.
https://www.ncbi.nlm.nih.gov/pubmed/15572415?dopt=Abstract This seems to suggest that DHT is not key to muscle growth.
Finisteride increases the risk of erectile dysfunction. Across studies, erectile dysfunction is reported in 3.4 to 15.8 percent of patients treated with 5mg of finasteride, compared to 1.7 to 6.3 percent treated with placebo.
Side effects of DHT inhibition https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4064044/
Erectile dysfunction and general sexual dysfunction.
In female to male transexuals, giving dusteride in addition to T prevented the normal increase in lean body mass
http://onlinelibrary.wiley.com/doi/10.1111/j.1743-6109.2008.00909.x/full
- DHT may be required at a certain level to boost muscle mass
Unreferenced statement finisteride leaves "testosterone levels normal or even slightly elevated by about 10% to 20% as a result of the enzymatic block" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1472916/
How do we know what DHT does?
There are multiple lines of evidence, but one place to start is to look at males who were born with 5α-Reductase deficiency a condition that means they have a considerably reduced capacity to produce DHT. DHT is produced from Testosterone via the 5α-Reductase (5AR) enzyme. There are different kinds of 5AR, 5α-Reductase deficiency generally means a deficiency in Type 2 5AR, the kind usually found in the testes. It must be noted that this condition does not mean these males completely lack DHT, they still have type 1 and 3, so some DHT is still produced, albeit at a much lower level than in a regular male.
At birth and through early childhood they have a female appearance and either female looking, or ambiguous genitalia. This changes, however, at puberty, when a hormonal surge either creates enough testosterone, or enough DHT via the remaining
- They can produce sperm.
- They can have erections, but these tend to be weak.
- Gender identity is typically male (
- They do not become bald as adults.
- Voice deepens at puberty (unclear whether this is due to increased testosterone or the small amount of DHT produced)
In general, individuals with 5-ARD are capable of producing viable sperm
Dutasteride
Acts on all 3 types of 5AR. It can reduce DHT by up to 98%.
DHT can support the male reproductive system on its own (without Testosterone, without Estrogen, without LH)
http://www.jsm.jsexmed.org/article/S1743-6095(15)30564-6/pdf
Elderly men were given DHT gel for two years. This increased serum DHT, but lead to complete suppression of LH, Teststerone and Estrogen. Sexual function remained normal.
Exogenous DHT improves sexual function in elderly men with poor sexual function, despite suppressing T
https://academic.oup.com/jcem/article-lookup/doi/10.1210/jcem.87.4.8138
Actions of Testosterone
Actions of DHT