This is a great question.
Yes, testosterone replacement shuts down LH and FSH, which shuts down the production of testosterone and sperm by the testicles. So the testicles' Leydig cells start losing volume due to inactivity. They do not die off, they just hibernate and lose size. The testosterone inside of the testicles also decreases which further decreases their size.
HCG mimics LH. It has been shown to make Leydig cells produce testosterone. It has also been shown to increase the amount of testosterone inside the testicles (Intratesticular testosterone or IT). The use of HCG alone to increase testosterone is not as popular as testosterone replacement due to several factors: 1- cost since large doses of HCG would be required, 2- quality of life of HCG alone vs TRT may be worse (this has not been validated by comparison studies), 3- concerns about long term high dose HCG use and its potential effect on desensitization of Leydig cells to it.
When used in small doses 2-3 times per week along with testosterone replacement, HCG can reverse the decrease of intratesticular testosterone. HCG's effect as a LH mimicker plus its ability to increase IT seem to be the reasons why men were able to preserve fertility (normal sperm) when using testosterone replacement plus
500 IU HCG every other day in Dr Lipshultz' study. The main surprising result of that study is that normal sperm quality can be preserved by this combo even in the absence of FSH, a gonadotropin thought to be essential in sperm production.
I would love to see a study that compares men using 2000-3000 IU of HCG per week to men using 500 IU 2-3 times per week +TRT monitoring their testicular size, sex drive and sperm quality over 6 months. That study would prove what we already know but will provide needed data for insurance reimbursement.
Print the attached study from Lipshultz et al that shows that HCG+TRT was able to preserve fertility in men. I am trying to get them to publish an extension of that data so that we also see the effect of quality of life and sex drive in these men.
This is an emerging field and unfortunately very few medical groups publish their results. I have been advocating for DR Lipshultz to also publish quality of life and sex drive data in men using TRT+ HCG since anecdotally know that HCG may boost sex drive in men on TRT alone. Testicular size is also increased back to baseline. However, these two anecdotal findings need to be validated by published data before insurance companies take this combination seriously.
More on HCG here:
https://www.excelmale.com/forum/sho...e-Testicular-Shrinkage-and-Preserve-Fertility