Author Gyno and I and E mechanisms.
Animal
Joined: Dec 03, 2001
Posts: 557
From: Parts unknown
Posted: 2001-12-03 17:02
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Don't believe anybody who tells you that nolvadex (Tamoxifen) doesn't lower IGF-1 levels as you can see in the last sentence.
The effects of the steroid hormones differ by organ site. The mitotic rate of the endometrial cells lining the uterus is stimulated by estrogen and inhibited by progestins. Breast tissue undergoes cell proliferation and loss in concert with the ovaries= cyclic production of estrogen and progesterone.[115] The role of estrogen as a primary stimulant of breast cell proliferation, which contributes to the development of breast cancer, is supported by epidemiologic studies, animal studies, and clinical trials.[112,114]
In addition, the simultaneous presence of progesterone probably further increases the rate of breast cell proliferation.[112] Although progesterone has inhibitory effects on the endometrium, evidence is accumulating that it increases the rate of cell division in breast tissue beyond that of estrogen alone.[118] Because the combined presence of estrogen and progesterone in oral contraceptives has stimulatory effects on breast cell proliferation, a protective effect against breast cancer is not anticipated, nor
has such an effect been seen.[116,118] Tamoxifen citrate is a nonsteroidal compound that exerts both estrogen agonistic and antagonistic effects. Acting as an antiestrogen in the breast, tamoxifen increases breast cell growth inhibitory factors, such as transforming growth factor beta
(TGF beta) and reduces stimulatory factors, such as transforming growth factor alpha (TGF alpha) and insulin like growth factor 1 (IGF 1).[147,148] Estrogen stimulates the growth of breast tumor cells by increasing the levels of growth stimulatory factors, such as TGF alpha.[147,148]