Re #2, in the mtf trans experience high estrogen and low testosterone are correlated with low libido, with some individuals even temporarily stopping antiandrogen medications in order to get some back
Yeah, your comment squares with (and the GP's point #2 contradicts) what I learned in my college Science & Gender class, which was a combined neuroscience/psychology offering where we read a bunch of papers. Most of them supported that testosterone was the primary driver of libido in both men and women, with higher T levels corresponding to higher sexual desire and lower T levels corresponding to the opposite.
E2 as a libido regulator is a cross-species conserved effect.
The landmark study in humans for this is the Finkelstein 2013 paper [0] -- they gave humans Testosterone with and without AI to block aromatization to E2. In the AI group, sexual desire and erectile function declined markedly across the board, even when they were given high doses of testosterone.
Then you have studies like [1] and [2]:
> "Both estradiol (E) and dihydrotestosterone (DHT) contribute to the activation of mating, although E is more important for copulation and DHT, for genital reflexes."
> "We show here that a single injection of estradiol (500 μg/kg) rapidly and transiently activates copulatory behavior in castrated male quail pre-treated with a dose of testosterone behaviorally ineffective by itself."
The underlying theme is that across animal species, estrogens are regulators of sexual desire/libido while androgens support the necessary biological functions (erection) required.
Unfortunately, anti-androgens have myriad effects beyond basic T suppression.
There are two primary drivers behind why anti-androgens would cause loss of libido beyond effect on T:
1) AA's cause androgen receptor blockade systemically. This blocks action at the AR that would be residual across systems from adrenal production. Most important for libido are the AR activity that occurs inside of neurons and astrocytes in the brain
2) AA's have a two-punch effects on the Prolactin/Dopamine system + Progesterone system. Chronically elevated prolactin causes down-regulation of dopamine, which by itself is enough to kill libido. Progestins modulate GABA, which can cause "flat affect" and "emotional flatlining".
The combo punch of neuronal/adrenal AR blockade + Prolactin/Dopamine dysregulation + GABA dysregulation would require a miracle to have preserved libido on.
It will depend exactly which anti androgen is used. I think you're describing the effects of cyproterone. Spironolactone has other side effects (a lot of them), while triptoreline targets the production of LH and FSH directly and seems to have fewer effects on other systems (though honestly it's a bit hard to tell)
libido is fixed with progesterone (which is commonly taken ~1-2 years into hrt) for better breast growth. anecdotally it makes you completely f*king feral