Regarding this androgen receptor downregulation thing, it's a myth like has been said. There was some study with testosterone on some human subjects... initially AR density increased but returned to baseline in 6 months. Who knows what happens with megadoses though.
What I do think happens with many pro's is severe insulin resistance. Huge doses of GH cause resistance, is further compounded by insulin use and to a smaller degree AAS use. I think this fucks up a body in the long run.