Withaferin-A, an anti-estrogen (and maybe also an anabolic) in ashwagandha
According to - predominantly sponsored - studies, ashwagandha supplementation increases testosterone levels and stimulates the development of muscle tissue. Researchers at the University of Pittsburgh Cancer Institute may have discovered in 2011 how ashwagandha can produce all those effects. Their research points to the pharmacological activity of withaferin-A, a prominent active ingredient in ashwagandha.Cancer inhibiting effect
Then the researchers exposed MCF-7 cells in test tubes to withaferin-A at concentrations of a few micromoles, the cells became less vital. In addition, withaferin-A damaged the DNA of the cells. MCF-7 cells are breast cancer cells that need estradiol to proliferate.

Anti-estrogenic effect

You would expect these kinds of effects in experiments in which researchers expose MCF-7 cells to anti-estrogens such as tamoxifen. So the researchers wondered whether withaferin-A had an anti-oestrogenic effect.To find out, the researchers put MVC-7 cells in test tubes with withaferin-A, and then measured what happened to the production of the estradiol receptor-alpha. This receptor provides the typical estrogenic effects of estradiol, such as the growth of adipose tissue in the breast region, water retention and aggression. The alpha-receptor is also involved in the growth of estradiol-sensitive cancer cell types.
The figure below shows that withaferin-A reduced the production of the estradiol receptor-alpha protein. This also happened if the researchers had added estradiol in addition to withaferin-A to their cancer cells.

Muscle building effect?
At the same time, withaferin-A also induced the production of estradiol receptor-beta, the researchers write. Via this receptor estradiol has anabolic effects in muscle and bone tissue and positive effects on the blood vessels.

According to German biochemists at the University of Cologne, ecdysterone, a steroid-like substance in spinach, has an anabolic effect because it activates estradiol receptor-beta.
Could withaferine-A and ecdysterone enhance each other's ergogenic effects?
A big thank you
This post came about thanks to Josh's scientific creativity. Josh, thank you.

Mol Carcinog. 2011 Aug;50(8):614-24.