[1] Conversion of estradiol into 2-hydroxyestradiol has also been detected in the uterus, breast, kidney, brain, and pituitary gland, as well as the placenta, and may similarly be mediated by cytochrome P450 enzymes.

[5] 2-Hydroxyestradiol is a catechol estrogen and in this regard bears some structural resemblance to the catecholamines dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline).

[6] The steroid is known to compete with catecholamines for binding to catechol O-methyltransferase and tyrosine hydroxylase and to directly and competitively inhibit these enzymes.

[6][7] In addition, 2-hydroxyestradiol has been found to displace spiperone from the D2 receptor with approximately 50% of the affinity of dopamine, whereas estradiol, estrone, and estriol and their other 2-hydroxylated and 2-methoxylated derivatives showed only weak or negligible inhibition.

[9] However, the researchers argued against this possibility because it was delayed (by several hours) and of relatively small magnitude, whereas established D2 receptor antagonists promptly induce marked increases in prolactin levels.

[9] The researchers concluded that the most likely explanation was that the increase was mediated by the estrogenic activity of 2-hydroxyestradiol, as similar increments in prolactin levels had been observed with estradiol.