Effect of aromatizable and unaromatizable androgen replacement in hypogonadal men on GH responsiveness.
OBJECTIVE
Although studies have clearly demonstrated that oestrogen replacement affects GH responsiveness by causing relative GH resistance, the effect of androgen replacement is unknown. Circumstantial evidence only suggests that androgen replacement may increase GH sensitivity and/or responsiveness. To examine the impact of androgens on GH responsiveness, hypogonadal men underwent the IGF-1 generation test in the unreplaced state, replaced with testosterone (T) and also replaced with dihydrotestosterone (DHT), its nonaromatizable metabolite.


METHODS
Twelve hypogonadal men with a normal GH axis were recruited. Each subject in random order had 4 weeks off T (NoRx), 4 weeks on T gel (TG) and 4 weeks on DHT gel (DHTG) applied daily, with 1 week washout between each preparation. An IGF-1 generation test using a subcutaneous injection of 7 mg of GH was performed at the end of each of these 4-week phases.


METHODS
Serum GHBP, total and free IGF-1, IGFBP-3 and acid-labile subunit (ALS) levels were measured at baseline and 24 h (peak) after GH administration.


RESULTS
Despite a decrease in GHBP during the TG and DHTG phases, there were no observed differences in baseline, peak or increment (peak - baseline) total or free IGF-1 between the NoRx, TG or DHTG phases.


CONCLUSIONS
There is no evidence of fluctuation in GH responsiveness in hypogonadal men, untreated or replaced with T or DHT alone. This implies that the increased level of oestradiol as a consequence of T replacement in hypogonadal men does not impact significantly on GH responsiveness, nor is there evidence of an androgen effect with elevated DHT levels as a consequence of either T or DHT replacement.
Department of Endocrinology, Christie Hospital, Wilmslow Road, Withington, Manchester, M20 4BX, UK. helena@kgleeson99.freeserve.co.uk
Helena K
HK
Gleeson
Stephen M
SM
Shalet
D000328:Adult; D000728:Androgens / Q000097:blood; D013196:Dihydrotestosterone; D020249:Hormone Replacement Therapy / Q000379:methods; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D007006:Hypogonadism / Q000188:drug therapy* / Q000503:physiopathology; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011994:Recombinant Proteins; D013739:Testosterone / Q000097:blood
D000728:Androgens; D018972:Insulin-Like Growth Factor Binding Protein 3; D011994:Recombinant Proteins; D013196:Dihydrotestosterone; D019382:Human Growth Hormone; D013739:Testosterone; D007334:Insulin-Like Growth Factor I