This an excellent study. The chart here seems to be the meat of it for our discussion:
Also, what about the effect on estradiol? I'm assuming hCG stimulates aromatase in the leydig cells, but how? Is it simply a matter of conversion from T to E2 via aromatase, as with exogenous testosterone? If that's the case, then why are conversion levels typically higher (say others) when it comes to hCG injections compared to testosterone injections? If this higher conversion is true, it'd probably be safer to aim for smaller daily injections rather than bigger injections less frequently.
Although there is still a ton of research to be done on the topic, a logical (to me) explanation for the effects that hCG can have on estradiol levels goes something like this...
-Since hCG is an LH analog, the testes end up receiving a higher-than-normal (and usually a more constant) "LH pulse".
-The increase in LH leads to an increase of intratesticular testosterone (ITT). ITT is far more "abundant" than serum testosterone. After all, the testes are where we naturally produce the hormone.
-In humans, the consensus is that the Leydig cells are the primary source of aromatase activity in the testes. It is also believed that there is aromatase activity within the Sertoli and germ cells...with some recent research showing that there may be quite a bit more activity there than previously thought.
-If ITT production is kicked into high gear by hCG, it makes sense that the intratesticular aromatase would follow suit.
-Since exogenous testosterone does not stimulate the production of ITT like hCG does (it does the opposite, via HPTA suppression), the bulk of the aromatase that's left to convert T-->E is the stuff that's found in peripheral tissues...or outside of the testes. This may be why the conversion of T-->E is less pronounced in men solely on testosterone.
-In men who use testosterone and
hCG, both sources of aromatase should technically be available to carry out their duties. Don't feel like you have to take the above as gospel, but it definitely makes the most sense to me.