Upon seeing a trans woman Facebook friend of mine's status noting that her feet had shrunk since she'd started HRT, I did a little research. I posted about it on Facebook, but I'm not sure anyone cared. Since I'd like to have easy access to my little summary in the future, I'll repost it here.
GnRHa (Gonadotropin Releasing Hormone agonist, a synthetic peptide that mimics Gonadotropin Releasing Hormone, which is female sex hormone that spikes during ovulation to trigger the release of LH and FSH) administration in transitioning MTF people is responsible for a decrease in bone density. GnRHas bind to GnRH receptors (GnRHR) like GnRH does, but fails to actually stimulate the receptor for longer than a few days. That results in the inhibition of LH, which stimulates the testes to synthesize testosterone. In my understanding, GnRHas bind to the GnRHRs in the pituitary, inhibiting gonadal testosterone synthesis but having no effect on adrenal testosterone, which is why it’s only sometimes administered alongside antiandrogens like spironolactone or cyproterone acetate (which is apparently not sold in the States…) to enhance the effects of HRT. But antiandrogens have interesting side effects, one of which is a loss of bone density.
GnRHa (Gonadotropin Releasing Hormone agonist, a synthetic peptide that mimics Gonadotropin Releasing Hormone, which is female sex hormone that spikes during ovulation to trigger the release of LH and FSH) administration in transitioning MTF people is responsible for a decrease in bone density. GnRHas bind to GnRH receptors (GnRHR) like GnRH does, but fails to actually stimulate the receptor for longer than a few days. That results in the inhibition of LH, which stimulates the testes to synthesize testosterone. In my understanding, GnRHas bind to the GnRHRs in the pituitary, inhibiting gonadal testosterone synthesis but having no effect on adrenal testosterone, which is why it’s only sometimes administered alongside antiandrogens like spironolactone or cyproterone acetate (which is apparently not sold in the States…) to enhance the effects of HRT. But antiandrogens have interesting side effects, one of which is a loss of bone density.
Testosterone and estrogen are both involved in the maintenance of regular levels of osteogenesis, so there are a bunch of interesting studies on the increased threat of osteoporosis and other weak bone diseases in individuals with hypogonadism (including various intersex conditions). Anyways, unless you take enough Estrogen, if you’re on T-blockers for too long, your bones start to suffer. I’m not sure whether Estrogen on its own would cause a decrease in bone density, but it makes sense that testosterone would be more active in stimulating bone growth. So I’d be fascinated to hear a greater explanation of the effects of estradiol/antiandrogens/GnRHa on bone density.
(This article is a little strange – it refers to trans women as men and apparently suggests that GnRHas should just replace estrogen entirely? I'm not sure how that's supposed to work, but it’s an interesting read.)
http://www.eje-online.org/content/153/1/107.full.pdf
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