Estradiol

Estradiol, or more precisely, 17β-estradiol, is a steroid and estrogen sex hormone, and the primary female sex hormone. It is named for and is important in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is essential for the development and maintenance of female reproductive tissues but it also has important effects in many other tissues including bone. While estrogen levels in men are lower compared to women, estrogens have essential functions in men as well. Estradiol is found in most vertebrates as well as many crustaceans, insects, fish, and other animal species.

Estradiol or oestradiol (American or British English usages), derives from estra-, Gk. οἶστρος (oistros, literally meaning "verve or inspiration") and -diol, a chemical name and suffix indicating that this form of steroid and sex hormone is a type of alcohol bearing two hydroxyl groups.

Estradiol is produced especially within the follicles of the female ovaries, but also in other endocrine (i.e., hormone-producing) and non-endocrine tissues (e.g., including fat, liver, adrenal, breast, and neural tissues). Estradiol is biosynthesized from progesterone (arrived at in two steps from cholesterol, via intermediate pregnenolone). One principle pathway then converts progesterone to its 17-hydroxy derivative, 17-hydroxyprogesterone, and then to Δ⁴-androstenedione via sequential cytochrome P450-catalyzed oxidations. Action of aromatase on Δ⁴-androstenedione generates estrone, and action of a dehydrogenase on this gives the title compound, 17β-estradiol. Alternatively, Δ⁴-androstenedione can be converted into the androgen, testosterone, which in turn can be converted directly into 17β-estradiol.

Alfatradiol

Alfatradiol (INN, or 17α-estradiol, trade names Ell-Cranell Alpha and Pantostin in Germany) is a 5α-reductase inhibitor used topically for the treatment of androgenic alopecia (hair loss) in men and women. It is a stereoisomer of the endogenous steroid hormone 17β-estradiol.

Uses

Alfatradiol is used in form of an ethanolic solution for topical application on the scalp. Similarly to other drugs against alopecia, topical or oral, it has to be applied continuously to prevent further hair loss. Regrowth of hair that was already lost is only possible to a limited extent. In general, advanced alopecia does not respond well to medical treatment, which has historically been thought to be a consequence of the hair roots being lost.

A university-led study (including several authors who are advisors to companies such as Pfizer) in 103 women comparing alfatradiol to minoxidil, another topical hair loss treatment, found the latter to be more effective. In contrast to minoxidil, alfatradiol did not result in an increase of hair density or thickness, but only in slowing down or stabilization of hair loss in this study. In an earlier study, no systemic side effects were noted, and 17α-estradiol was found to reduce androgenic hair loss, though it was not effective at growing new hair.