First, shut down is a misleading term. One is never "shut down", even when using Deca at 600mg for 20 weeks.
Lh an fsh are both suppressed, but production still goes on.
Without getting into specifics, dhea is a sex hormone produced, and from there, andro-dione/diol is produced, then estrogen or test can be produced, and again, estrogen can be made, or dht.
Still following. Good.
The htpa axis's job is to keep everything in balance.
When you use exogenous hormones, especially ones that bind strongly to the androgen receptor ( like Epi )
The htpa senses this surge/imbalance in androgens, and will do two things, (well, a whole bunch of hormones get all whacked out, but that's too much to discuss on my phone) ,
It will slow production of androgens and increase production of aromatase, all in an attempt to balance out the androgen:estrogen ratio/balance.
When taking non aromatizable steroids, this should happen to a higher degree.
Because now, with production of aromatizable androgens slowed, and the supraphysiological amounts of non aromatizable androgens in the system, the body will then attempt to fix this imbalance.
How, by converting the andro an test that's being produced still, into estrogen.
This isn't even getting into the entire line of other hormones all thrown out of wack from introducing supraphysiological dosages of synthetic androgens into your system