Estrogen-like effects of 7,12-dimethylbenz(a)anthracene on the female rat hypothalamo-pituitary axis

Abstract

We have recently demonstrated that 7,12-dimethylbenz(a)anthracene (DMBA), a potent inducer of mammary tumors in rodents, can in vitro decrease the number of membrane dopamine D₂ receptors and stimulate prolactin (PRL) release, by direct estrogen-like actions on anterior pituitary. In the present study, we tested the ability of DMBA to mimic the in vivo estradiol (17βE₂) effects on pituitary D₂ receptors and on PRL as well as LH release. We have found that DMBA, like 17βE₂, when injected to ovariectomized rats, induced a decrease in the number of anterior pituitary D₂ receptors, a release of PRL and exerted a biphasic (acute negative and longer term positive) action on LH secretion. We thus examined the ability of DMBA to interact with 17βE₂ receptors in the hypothalamo-pituitary axis: DMBA binds to the pituitary cytosolic estrogen receptors with an affinity 0.001% that of 17βE₂. Finally [³H]DMBA binds to hypothalamus-containing brain sections. This binding was displaced partially by RU 2858 a pure estrogen agonist and totally by tamoxifen, a purported estrogen antagonist. No competition for [³H]DMBA binding was observed with an androgen (RU 1881) or a glucocorticoid (RU 26988) agonist.

From these data, it may be concluded that DMBA can act as a partial estrogen in pituitary and hypothalamic tissues.