Sex steroids and the growth hormone/insulin-like growth factor-I axis in adults.
In healthy adults insulin-like growth factor (IGF)-I levels do not differ between males and females, whereas spontaneous growth hormone (GH) secretion is approximately twofold higher in females. Untreated GH-deficient (GHD) women exhibit lower IGF-I levels compared with men and the increase in serum IGF-I during GH replacement is also significantly less. These data suggest a resistance to GH in women, which in healthy subjects is compensated for by increased GH secretion. Administration of oral oestrogen in healthy postmenopausal women suppresses hepatic IGF-I production and increases pituitary GH release, and oral oestrogen replacement in women with GHD lowers IGF-I concentrations and increases the amount of GH necessary to achieve IGF-I target levels during treatment. These data clearly suggest that hepatic suppression of IGF-I production by oestrogen subserves the gender difference in GH sensitivity, but it is also likely that sex steroids may interact with the GH/IGF axis at other levels. There is also circumstantial evidence to indicate that testosterone stimulates IGF-I production and it is speculated that a certain threshold level of androgens is essential to ensure hepatic IGF-I production. Whether these data should translate into earlier discontinuation of oestrogen replacement therapy in women with hypopituitarism merits consideration.
Jørgensen
Jens O L
JO
Medical Department M (Endocrinology and Diabetes) and Department of Gynecology and Obstetrics, Arhus University Hospital, Arhus, Denmark. jolj@dadlnet.dk
Christensen
Jens Juel
JJ
Vestergaard
Esben
E
Fisker
Sanne
S
Ovesen
Per
P
Christiansen
Jens Sandahl
JS
D000172:Acromegaly / Q000097:blood* / Q000188:drug therapy; D000328:Adult; D015914:Estrogen Replacement Therapy / Q000009:adverse effects; D005260:Female; D012739:Gonadal Steroid Hormones / Q000502:physiology*; D019382:Human Growth Hormone / Q000172:deficiency* / Q000502:physiology*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D008297:Male; D017698:Postmenopause; D012737:Sex Factors
D012739:Gonadal Steroid Hormones; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I