Endogenous Estrogen Regulates Somatostatin-Induced Rebound Gh Secretion In Postmenopausal Women

Background: Systemic concentrations of T, estradiol (E-2), GH, IGF-1, and IGF binding protein-3 decline in healthy aging individuals. Conversely, T and E-2 stimulate GH and IGF-1 production in hypogonadal patients.Hypothesis: Because E-2 stimulates GH secretion, putatively via the nuclear estrogen receptor-a and E-2 and GH fall with menopause, we postulated that diminished endogenous E-2 contributes to low GH output in older women.Location: The study was conducted at the Mayo Center for Clinical and Translational Science.Study Design: This was a randomized, double-blind, controlled study in 60 healthy postmenopausal women treated with the following: 1) double placebo; 2) anastrozole, a potent inhibitor of aromatase-enzyme activity, which mediates E-2 synthesis from I; and/or 3) fulvestrant, a selective estrogen receptor-a antagonist.Methods: GH pulse generation was quantified by frequent GH sampling before and after shortterm iv somatostatin infusion, thought to induce hypothalamic GHRH-mediated rebound-like GH secretion.Results: On anastrozole, E-2 fell from 3.1 +/- 0.35 pg/mL to 0.36 +/- 0.04 pg/mL, and estrone from 13 +/- 1.4 pg/mL to 1.9 +/- 0.01 pg/mL (P <.001) by mass spectrometry. Estrogen values were unchanged by fulvestrant. I concentrations did not change. One-hour peak GH rebound after somatostatin infusion declined markedly during both estrogen-deprivation schedules (P < .001). Mean (150 min) maximal GH rebound decreased comparably (P < .001). Measures of GH rebound correlated negatively with computed tomography-estimated abdominal visceral fat (all P < .05).Conclusion: These data suggest a previously unrecognized dependence of hypothalamo-pituitary GH regulation on low levels of endogenous estrogen after menopause.