Estrogen-Like potentiation of ghrelin-stimulated GH secretion by fulvestrant, a putatively selective ER antagonist, in postmenopausal women

Context: Hyposomatotropism in healthy aging women reflects in part physiological estrogen (estradiol [E₂]) depletion associated with menopause. Objective and Design: The purpose of this study was to test the hypothesis that low concentrations of endogenous E₂ after menopause continue to drive GH secretion. Setting: The study was performed at the Mayo Center for Clinical and Translational Science. Participants: The participants were 24 postmenopausal women (aged 50-77 years with body mass index of 19-32 kg/m²). Interventions: This was a randomized, double-blind, placebo-controlled, parallel-cohort treatment study with placebo (PL) (n = 14) or the antiestrogen fulvestrant (FUL) (n = 10) for 3 weeks, followed by infusion of L-arginine with saline, GHRH, ghrelin, or both peptide secretagogues. Outcomes: GH concentrations were measured over 6 hours with 10-minute sampling and mass spectrometry measures of testosterone, E₂, and estrone. Results: Concentrations of testosterone, E₂, estrone, SHBG, IGF-I, LH, and FSH were not influenced by antiestrogen treatment. In contrast, GH rose from 0.096 ± 0.018 (PL) to 0.23 ± 0.063 μg/L (FUL, P = .033), and IGF-I binding protein type 3 (IGFBP-3) from 3.6 ± 0.18 to 4.0 ± 2.0 mg/L (P = .041). Conversely, prolactin fell from 7.1 ± 0.69 (PL) to 5.5 ± 0.57 μg/L (FUL) (P = .05), and IGF-I binding protein type 1 (IGFBP-1) fell from 44 ± 9.4 to 27 ± 4.3 μg/L (P = .048). Moreover, FUL vs PL potentiated mean GH responses to L-arginine/saline (P = .007), L-arginine/ghrelin (P = .008), and L-arginine/GHRH + ghrelin (P = .031), but not L-arginine/GHRH. Conclusion: The potent antiestrogen, FUL, amplifies fasting and secretagogue-driven GH secretion and IGFBP-3 concentrations in postmenopausal women without altering SHBG or sex steroid levels. FUL also suppresses prolactin and IGFBP-1, without altering IGF-I. Thus, a major antiestrogen mediates 3 actions of estrogen: agonism (GH), neutral effects (sex steroids), and estrogen antagonism (prolactin and IGFBP-1).