There is no substitute for Testosterone. Aromatase inhibitors will not change your endogenous T levels (unless of course your endogenous Androgen have been a little higher and thus have also been being converted by the same process into Estrogen instead. But that would be the sole exception to my knowledge). Beyond that you would need to consult with an Endocrinologist to further discuss the benefits and potential drawbacks to make an informed decision.
Essentially, it is the precursor hormone DHEA (Dehydroepiandrosterone; a weak androgen) which is converted or synthesized by Aromatase into Estrogen (and a negligible amount of this process happening directly within the Adrenal Glands explaining why they also produce a small amount of both Estrogen but also Testosterone locally; however that amount is INSUFFICIENT on its own; enter the necessity of HRT in the absence of gonads). In general, if that action is not possible (inhibited) then neither Dehydroepiandrosterone nor Testosterone (but excepting Dihydrotestosterone) can be converted by Aromatase into Estrogen. As to how it will feel, I can't comment as I've never been on them (although I personally feel it should be a combination for FTM's owing to how easily excess Androgen can and will be converted to Estrogen but I digress). I imagine the rule of "it's different for everyone" applies to this just the same as does the swapping out of one for the other.
I now feel the necessity to clarify a lesser-known point of fact. It is not just the sharp decline of Estrogen alone in those who have had an Oophorectomy which is in itself responsible for the accompanying and significantly increased risks of Osteoporosis. In reality the culprit is a coordinated and significant decline between Estrogen AND Progesterone (and to a lesser extent ALSO the decline of Androgen, being that the Ovaries also produce the lion's share of it in females). The Adrenal Glands have always and always will only ever make a SUPPLEMENTARY amount of your erstwhile sex hormones/steroids; they only make what little they do within themselves because they are responsible for creating the preliminary hormones (by and large, these include DHEA in addition to the Progestogens) that will later become your Estrogen and/or Testosterone under further conversions in your Ovaries/Testis, also including your Progesterone (that seldom lauded one that plays both fields; is largely neither male nor female). A little bit of that happens within the Adrenal Glands BUT NOT ENOUGH, hence the necessity of the specifically male or female gonads.
My grandmother in example had Oophorectomy and Hysterectomy at age 20 (back then patients actually had a lot more deciding factor in their care; they weren't as easily overridden... pity we've lost that down the line. These days it is almost impossible to get those procedures done without exceptional circumstances forcing their eventuality. I know, I'd asked and was promptly denied, getting that "But what if you want babies?! We can't do that!" Argh. I was even informed I would be hard-pressed to find a surgeon willing to remove "healthy organs" even out of pocket. Anyway, I digress again) she has Osteoporosis now and I am convinced it is directly because she's also not been taking replacements for either Estrogen or Progesterone for about 34 years now (first 25 she had but she stopped for whatever reason). Very stupid decision but that IS her right nonetheless. Although, who knows... perhaps the synthetic stuff would have had negative cardiovascular effects by now if she had (important also to disclose that that risk is equal between synthetic Estrogen and Testosterone; consult the drug facts slip if you must. In fact, birth control pills could be argued the most dicey being that there have been so many more incurring the odd infarction here or there on them than compared against the other two. Most probably because they add more than necessary amounts of the hormones in those which still are producing their own, so it's too much altogether. Or so that's my educated theory).
So, 'E blockers' alone will not dramatically increase the risks of Osterpersosis just so long long as you are still manufacturing the necessary Progesterone until or unless you are able to later get on Testosterone. If however you are for whatever reason deficient in Progesterone and then also block your Estrogen, you would and only then be at similar high risk of Ostereopersosis as an elderly, postmenopausal woman (I'll hasten to add that has also had Oophorectomy) but which is refusing HRT. That's not where you want to be.
This same statement applies to transguys that have had Oophorectomy and stop their T for prolonged periods as well (in which case I'd say to them, go get Progesterone replacement at the very least). It's not good for anyone to be without at least one of these three hormones and at normal level. My grandmother hasn't been feeling right for about twenty years now and this is the reason why (every test she makes her GP do is normal; she just refuses to believe her not being on HRT is the reason for her feeling crummy. Bully for her). Her body wants one of the three at substantial level and it simply just isn't there in the amount it wants (and incidentally, needs). That has consequences and she's definitely reaping 'em. Makes me want to slip them to her but that's illegal, so... *sigh*
