Estrogen Conversion and Receptors

The main feminizing effects of estrogen depend on sex-hormone receptors being present in cells and hormone molecules being free to bind to them to affect gene expression. Since sex-hormones also regulate receptor expression, increasing the amount of receptors or hormone available for binding is thus a desirable goal for feminizing HRT.

Estradiol has a pathway of being synthesized from testosterone in the body through an enzyme called aromatase which allows for certain levels of testosterone to circulate and still be converted to estrogen.

This conversion of sex-hormones has an important effect on sites such as the breasts, fat, bones and brain which are affected by local synthesis of estradiol acting directly on the tissues.