title: Sex steroids and the growth hormone/insulin-like growth factor-I axis in adults.
abstract: 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.
authors.affiliation: Medical Department M (Endocrinology and Diabetes) and Department of Gynecology and Obstetrics, Arhus University Hospital, Arhus, Denmark. jolj@dadlnet.dk
authors.forename: Jens O L
authors.initials: JO
authors.lastname: Jørgensen
authors.forename: Jens Juel
authors.initials: JJ
authors.lastname: Christensen
authors.forename: Esben
authors.initials: E
authors.lastname: Vestergaard
authors.forename: Sanne
authors.initials: S
authors.lastname: Fisker
authors.forename: Per
authors.initials: P
authors.lastname: Ovesen
authors.forename: Jens Sandahl
authors.initials: JS
authors.lastname: Christiansen
mesh_terms: 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
chemical_list: D012739:Gonadal Steroid Hormones; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I