Morning versus evening administration of estradiol to girls with Turner syndrome receiving growth hormone: impact on growth hormone and metabolism. A randomized placebo-controlled crossover study

Timing of 17beta-estradiol (E2) administration in relation to that of GH could influence the "first pass effect" of E2 on hepatic IGF-I secretion. In order to test this hypothesis, a randomized double-blind placebo-controlled crossover study was conducted. Nine Turner girls (12.8-20.0y) were treated for 2 mo periods with GH 0.1 IU/kg/d sc at bedtime, and oral E2 6-11 microg/kg/d in the morning and placebo in the evening in one 2-mo period and vice versa in the other period. After each period, 24-h blood sampling was performed. IGF-I and mean 24-h integrated GH were comparable. However, the IGF-I/IGFBP-3 ratio was higher (p = 0.05) and insulin levels were lower after evening administration of E2 (24 h: p = 0.03). During an oral glucose tolerance test in the morning, glucagon and insulin were lower following evening E2 administration (ANOVA: glucagon, p = 0.03; insulin, p = 0.04), as well as insulin resistance tended to be lower (p = 0.09). CONCLUSION: The timing of oral E2 supplementation modulates the IGF-I/IGFBP-3 ratio, insulin and glucagon levels in Turner syndrome during GH treatment, Evening administration of oral estrogen together with evening injections of GH may be preferable.