The term antiandrogen, as defined by Dorfman, implies prevention of expression of androgen activity at target sites and does not include other mechanisms of decreasing androgen action, such as a decrease in production of androgens, interference with androgen metabolism, or change in androgen plasma protein binding.
An anti androgen, simply put, is a compound (usually a synthetic pharmaceutical), which blocks or otherwise interferes with the normal action of androgens at cellular receptor sites. There are two main types of anti-androgen: non-steroidal anti-androgens and steroidal anti-androgens. However, there is a third type that is often overlooked, the indirect anti androgen.
Topical estrogen
Estrogens are indirect anti androgens, increasing the production of sex hormone binding globulin (SHBG) and thus leading to a decrease in the bioactive free testosterone. SHBG, a glycoprotein synthesized by the liver, is the most important protein for androgen binding. The more potent androgens and estradiol are bound in the plasma to SHBG, although the binding affinities differ. Elevated testosterone causes SHBG synthesis to decrease, in addition to an increased activity of 5 alpha – Reductase, the enzyme responsible for the metabolism of testosterone to DHT. Estrogens increase Sex hormone binding globulin (SHBG) and thus further decrease the amount of free testosterone.
Extensive clinical trials of the use of a topical estrogen preparation in subjects with androgenetic alopecia have been not been conducted as yet. However, one double-blind, controlled, 6-month trial of topical 0.025% 17 alpha – estradiol conducted with 51 men and women who had pattern alopecia showed a significant reduction in the percentage of telogen hairs along with stabilization of the hair loss. Although more than 70 percent of a topically applied preparation is metabolized to weak non-androgenic by-products, the absorption of topical estrogen can lead to decreased libido in men.
Topical estrogens are not generally available in North America, but they are being used in Europe and topical estrogen products are available from a number of pharmaceutical companies there. There seems to be some confusion over which estrogen formulation is best (as there are different types of estrogen) but it seems that estrogen application topically could help treat pattern baldness in both men and women.