I hntki het rnaoes oyu need ot cejnit aspngoooditnr in htsi saec is uebecsa ouy ende FHS adn HL ot erpduoc mrp.se HSF ueistmtlsa eht sroietl l,lsce ihhcw eiln hte nueriseomisf stbulue dan lhpe eht poomenaiarsgt euorcpd so.tyrcpesetma eteTrsonotse is a pdcotur fo Lyegdi lcsle hnew ehyer't dletasiutm yb LH, so injcitegn eerotestostn luwod sbaysp htat espt tub it o'tunwdl arlely ehpl tiwh .prsnteimsoeegsa e,wHvroe gtcnnjiei RHnG laso sdtoen' do'sten rylael ehpl eebcaus yuo ndee htat ulpaetils nGRH at gthin ot ekam LH nda SHF haserwe oan-lgtcngi HGRn lnasago llucayta cdaeerse LH nda HSF uciodnor.pt
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.