Progesterone blockers do not help against gyno due to nandrolone decanoate (Tamox will)

The progesterone blocker RU486 does not help against gynecomastia - in short: gyno - by nandrolone decanoate or other 19-nor-androgens. You can deduce that from some older research by the pharmaceutical company Theramex.
Nandrolone decanoate converts to estradiol five times more difficult than testosterone. We have known this since the 1950s, when one of the researchers drew up the table below based on test tube studies. [1] 19-nor-testosterone is nandrolone.

However, doping gurus know that steroids that are more difficult to convert into estradiol than testosterone, such as deca, can still cause gyno. And they also have an explanation for it. "These drugs sometimes work like progestagens," Nelson Montana writes, for example. [2] "They link to the progesterone receptor, and progesterone increases the breasts of women. It is therefore logical that progesterone-like steroids do the same for men. "
The solution, you would say, is the use of anti-progestagens such as RU486. This is the most powerful progesterone blocker on the market today and attaches so much importance to the progesterone receptor that it completely displaces progesterone. But years ago, Théramex discovered that progesterone blockers cannot prevent gyno due to 19-nor-androgens.
In a study published in 1995, the researchers tested the estrogenic effect of a series of progestagens, and included a set of derivatives of 19-nor-testosterone. Not so long ago [3] they have summarized the results from that research in the table below. The numbers indicate the estrogenic effect of 19-norT = nandrolone and NEL, NGM, LNG, NETA = nandrolone relatives. The table gives the estrogenic effect at two concentrations, and compares it with the estrogenic effect of estradiol. It is automatically set to 100.

As you can see, all androgens within the progestagens have an estrogenic effect. In some of them the effect exceeds that of estradiol. At extremely high concentrations, at least. The above involves tests with cells in a test tube, in which the researchers measured an enzyme that the cells started to produce after stimulating the estrogen receptor.
The researchers wondered what caused this estrogenic effect. [4] Did it have to do with the progesterone effect of the 19-nor drugs? To find out, they repeated the tests, but also put the RU486 progesterone blocker in the test tubes. They did the same with the anti-estrogen 4-hydroxy tamoxifen. The figure below shows what happens with the production of the enzyme. The 19-nor-androgen used was norethindrone.

As you can see, addition of the progesterone blocker did not affect the production of the enzyme. Progesterone activity therefore has nothing to do with the estrogenic effect of 19-nor-androgens. Addition of the anti-estrogen indeed reduced the production of the enzyme does .
The researchers repeated the tests with aminoglutethimide, a substance that is guaranteed to stop all aromatase. That had no effect. The estradiol effect therefore has nothing to do with aromatase.

But what causes the estrogenic effect? The researchers don't know. Not anymore, at least. In their 1995 publication, they suggest that it is caused by unknown metabolites of the androgens. In their more recent publication from 2003, however, they leave open the possibility that 19-nor-androgens can behave themselves as estrogens.
Anyway: the conclusion for athletes is clear. Anti-Prostegans do not help against Gyno by Deca. Antiestrogens such as tamoxifen do.
1. Kenneth Ryan. Biological Aromatization of Steroids. J. Biol. Chem., Feb, 1959; 234: 268 - 272.
2. Nelson Montana. Oh no! It's Gyno! What can you do about it? Testosterone Magazine via, nr 111, 30-6-2000.
2. J. Shields-Botella, I Duc, E. Duranti, F. Puccio, P. Bonnet, R. Delansorne, J. Paris. An overview of nomegestrol acetate selective receptor binding and lack of estrogenic action on hormone-dependent cancer cells. Journal of Steroid Biochemistry & Molecular Biology 87 (2003) 111-122.
3. J. Botella, E. Duranti, V. Viader, I. Duc, R. Delansorne, J. Paris. Lack of Estrogenic Potential or Progesterone-or 19-Nor-progesterone-derived Progestins as Opposed to Testosterone or 19-Nor-testosterone Derivatives on EndometrialIshikawa Cells. Steroid Biochem. Molec. Biol. Full. 55, no. 1, pp. 77-84, 1995.