what you's think of this

"Without the powerful Dopamine nervous function, Anabolic and TRT will trigger the brain's testosterone negative feedback controller to shut down your hypothalamus-pituitary-testicular axis, resulting in weak testosterone and sperm productions in the testicles. Thus, you are prescribed to use the HCG (human chorionic gonadotropin) drug to stimulate your pituitary LH for your testosterone production and thyroid function.
Without the powerful acetylcholine nervous function, your adrenal function will go low, resulting in DHEA and androstenedione deficiency, frequently triggering the sympathetic function for "flight or fight" which includes stress, anxiety, restless, erectile withdrawal and premature ejaculation during lovemaking, and weakening the parasympathetic nervous function for healing, energy restoration and penile erection.
Without the powerful serotonin nervous function, Anabolic, TRT and HCG causes short temper, impatience, mood swing, sleeping disorder (deficiency of melatonin during the night due to less serotonin-melatonin conversion), and emotional instability. The serotonin nervous system is a modulator of the sympathetic nervous function and a regulator of the dopamine/norepinephrine - epinephrine (adrenalin, the stress "flight or Fight" hormone).
Your body won't get sufficient energy recharge without a proper brain's acetylcholine/parasympathetic nervous functions for a hard erection, and won't preserve enough energy for a persistent, hard erection for a long lovemaking session without a proper serotonin nervous function."

also
Why TRT doesnt help erections

"1. The testosterone level varies from time to time during the day and night, it reaches its peaks at around 5 AM (highest peak) 10 AM (2nd peak), and 5 PM (3nd peak) and its troughs at 8 PM (lowest trough) and 2 PM (2nd trough).
The testosterone level of 245 indicates your testicular failure.
A performance testosterone level is around 600-900 ng/dl.
The 900 level is about the puberty boy's.
The sources of testosterone: Testicular function (about 70-90%), Adrenal function (about 10-15%), and brain and organ tissues (about 5-10%).

2. If you can not power your liver P450 detoxification system to reduce the production of the liver enzyme aromatase, testosterone replacement therapy will increase your estrogen level, instead of your testosterone level.
You need a liver detoxification and the brain's acetylcholine/parasympathetic nervous action to correct the liver P450 system.

3. A low LH level means: Your brain's dopamine nervous function is too weak to drive your pituitary function for the release of LH and FSH in stimulating your testicular function."

its from some dr. lin from linplaza.com