Serum Insulin-Like Growth Factor I Levels in Growth Hormone-Deficient Adults: Influence of Sex Steroids

Abstract

Measurement of serum insulin-like growth factor I (IGF-I) concentrations remains the single most important tool in the evaluation of growth hormone (GH) replacement in GH-deficient adults, and the therapeutic goal is to maintain the level within the age-adjusted normal range. In healthy adults, IGF-I levels do not differ between males and females, whereas spontaneous GH secretion is approximately twofold higher in females. Untreated GH-deficient women exhibit lower IGF-I levels compared with men, and the increase in serum IGF-I during GH replacement is also significantly less. Put together, these data suggest resistance to GH in women, which in healthy individuals is compensated for by increased GH secretion. Administration of oral oestrogen in healthy post-menopausal women suppresses hepatic IGF-I production and increases pituitary GH release, and oral oestrogen replacement in women with GH deficiency lowers IGF-I concentrations and increases the amount of GH necessary to obtain 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 further 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 adult women with hypopituitarism merits consideration.

Low-dose growth hormone administration mobilizes endothelial progenitor cells in healthy adults

“…Our study population consisted of 10 individuals, four of whom were females. We may not have appreciated this IGF-1 mediated effect due to our smaller sample size, or due to the inclusion of females in our study population, as estrogen suppresses hepatic production of IGF-1 [35]. Further studies are indicated to better define both the IGF-1 modulation of CD34+, VEGFR2(KDR)+, and AC133+ cells in diverse populations and also the possible impact of the somatotropic axis on the late-outgrowth EPC population.…”

A prospective study of dairy foods intake and anovulatory infertility

“…Whole milk and other high-fat dairy products have a higher estrogen concentration than their low-fat counterparts (Wolford and Argoudelsi, 1979). Since estrogens decrease circulating IGF-I levels (Jorgensen et al, 2004;Veldhuis et al, 2005), it is possible that their presence in high-fat dairy foods could explain the observed association. Alternatively, increased insulin sensitivity among high-fat dairy consumers may have improved ovulatory function.…”

The value of IGF1 estimation in adults with GH deficiency

“…Recognized factors influencing IGF1 status in GHD patients include age (20), gender (13,(21)(22)(23)(24)(25)(26), exogenous estrogen therapy (27), and prolactin status (28).…”