Obviously the FSH -> spermatogenesis answer is the main idea, but I also think giving exogenous testosterone might actually impair levels of Testosterone in the testes as the concentration needs to be much higher in the testes for functionality due to a binding protein that is produced under stimulation by LH (which would be under neg feedback from exogenous testosterone)
I agree with below, sertoli cells release a testosterone binding protein in response to FSH in order to radically increase testosterone levels within the seminiferous tubules. That is why individuals who take exogenous testosterone have decreased fertility even while taking T.
so his pitutary adenoma was removed, so prolly gonadotrophs were removed with it, so if you give gnrh it won't do anything as it can;t produce FSH/LH so you give fsh/lh directly to indce spermatogenesis and testo synthesis.
submitted by โneonem(630)
I think the reason you need to inject gonadotropins in this case is because you need FSH and LH to produce sperm. FSH stimulates the sertoli cells, which line the seminiferous tubules and help the spermatogonia produce spermatocytes. Testosterone is a product of Leydig cells when they're stimulated by LH, so injecting testosterone would bypass that step but it wouldn't really help with spermatogenesis. However, injecting GnRH also doesn't doesn't really help because you need that pulsatile GnRH at night to make LH and FSH whereas long-acting GnRH analogs actually decrease LH and FSH production.