Hormonal Breast Augmentation: Prognostic Relevance of Insulin-Like Growth Factor-I,
Gynecological Endocrinology, 12:2, 123-127"In 21 women (46.7%), breast size increased from 824.3 ± 13.7 mm to 898.5 ± 12.5 mm after 6 months. In these women a significant increase in IGF-I values was noted after 4 weeks of treatment. The increase in IGF-I values was not statistically significant in the remaining women. In addition, treatment was not successful in these women."
"IGF-I concentration seems to be of prognostic value as far as the response of breast tissue to estrogen stimulation is concerned. If IGF-I levels do not increase within 1 month, treatment should be discontinued. If IGF-I values do increase, this indicates that treatment is likely to be successful and can therefore be continued."
GH stimulates IGF-1 and most its effects appear to be mediated through IGF-1. Estrogen when circulating through the liver, downregulates (reduces) IGF-1 production as opposed to androgen which upregulates it.
https://en.wikipedia.org/wiki/Hormonal_breast_enhancement"Systemic administration of GH or IGF-1 causes mammary hyperplasia (enlargement of the mammary glands) in animals.[21] For example, in a study of aged female rhesus macaques, treatment with GH alone, IGF-1 alone, and the combination of GH and IGF-1, were found to produce mammary gland hyperplasia and increased mammary gland size and epithelial proliferation by 2-fold, 3- to 4-fold, and 4- to 5-fold, respectively, changes that were directly correlated with serum concentrations of GH and IGF-1.[22][23][24] Accordingly, research has found that girls with growth hormone deficiency (GHD) who are treated with GH experience accelerated breast growth[25] and that boys with GHD treated with GH sometimes experience gynecomastia.[26] Moreover, IGF-1 levels and activity have been found to be correlated with breast volume in the female general population.[10]"
But,
"In women with Laron syndrome, where the growth hormone receptor (GHR) is defective and insensitive to GH and serum IGF-1 levels are very low, puberty, including breast development, is delayed, although full sexual maturity is always eventually reached.[27] Moreover, breast development and size are normal (albeit delayed) in spite of GH/IGF-1 axis insufficiency"
You can find lots of other useful information on this page but check references, as always.
I believe both estrogen and progesterone upregulate (increase) GH receptors in breast tissue.
https://en.wikipedia.org/wiki/Breast_development"The master regulators of breast development are the steroid hormones, estrogen and progesterone, growth hormone (GH), mostly via its secretory product, insulin-like growth factor 1 (IGF-1), and prolactin.[1]"
Etc.
Enjoy
and glad you're experiencing good results. Goes to show you that we are all different and some may do very well on low levels of E, despite higher T.
Also, this might interest you although how they define feminization and androgenization is flawed in some ways:
J Natl Med Assoc. 1992 Mar; 84(3): 241–250."Despite similar degrees of feminization in all 40 individuals in whom hormonal studies were performed, variable suppression of serum testosterone concentrations was present. Based on their testosterone concentrations while on feminizing hormone therapy, the transsexual inmates could be divided into three groups. In Group I (the "suppressed" group), the serum testosterone concentrations were markedly depressed (less than 10 ng/dL); in Group II (the "non-suppressed" group), the values of testosterone were normal (446 to 1072 ng/dL); and in Group III (the "intermediate" group), the testosterone values were between those of the suppressed group and the nonsuppressed group. We speculate that feminizing hormone therapy may induce the development of a state of target hormone resistance to testosterone that results in similar degrees of feminization independent of the circulating concentrations of testosterone."
