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Estradiol Regulates GH-Releasing Peptide's Interactions with GH

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Estradiol Regulates GH-Releasing Peptide's Interactions with GH C Norman and others GHRP, GHRH, and SS in women 170:1 121–129 Clinical Study Estradiol regulates GH-releasing peptide’s interactions with GH-releasing hormone and somatostatin in postmenopausal women Catalina Norman, Nanette L Rollene1, Dana Erickson, John M Miles, Cyril Y Bowers2 and Johannes D Veldhuis Correspondence Endocrine Research Unit, Mayo School of Graduate Medical Education, Center for Translational Science Activities, should be addressed Mayo Clinic, Rochester, Minnesota 55905, USA, 1Division of Reproductive Endocrinology, Naval Medical Center to J D Veldhuis Portsmouth (NMCP), Portsmouth, Virginia 23708, USA and 2Endocrinology and Metabolism Section, Peptide Email Research Section, Tulane University Health Sciences Center, New Orleans, Louisiana 70112, USA [email protected] Abstract Objective: Estrogen stimulates pulsatile secretion of GH, via mechanisms that are largely unknown. An untested hypothesis is that estradiol (E2) drives GH secretion by amplifying interactions among GH-releasing hormone (GHRH), somatostatin (SS), and GH-releasing peptide (GHRP). Design: The design comprised double-blind randomized prospective administration of transdermal E2 vs placebo to healthy postmenopausal women (nZ24) followed by pulsatile GHRH or SS infusions for 13 h overnight with or without continuous GHRP2 stimulation. Methods: End points were mean concentrations, deconvolved secretion, and approximate entropy (ApEn; a regularity measure) of GH. Results: By generalized ANOVA models, it was observed that E2 vs placebo supplementation: i) augmented mean (13-h) GH concentrations (PZ0.023), GHRH-induced pulsatile GH secretion over the first 3 h (PZ0.0085) and pulsatile GH secretion over the next 10 h (PZ0.054); ii) increased GHRP-modulated (PZ0.022) and SS-modulated (P!0.001) GH ApEn; and iii) did not amplify GHRH/GHRP synergy during pulsatile GH secretion. By linear regression, E2 concentrations were found to be European Journal of Endocrinology positively correlated with GH secretion during GHRP2 infusion (PZ0.022), whereas BMI was found to be negatively correlated with GH secretion during GHRH (PZ0.006) and combined GHRH/GHRP (PZ0.015) stimulation. E2 and BMI jointly 2 determined triple (combined L-arginine, GHRH, and GHRP2) stimulation of GH secretion after saline (R Z0.44 and PZ0.003) and pulsatile GHRH (R2Z0.39 and PZ0.013) infusions. Conclusion: In summary, in postmenopausal women, E2 supplementation augments the amount (mass) and alters the pattern (regularity) of GH secretion via interactions among GHRH, SS, GHRP, and BMI. These outcomes introduce a more complex model of E2 supplementation in coordinating GH secretion in aging women. European Journal of Endocrinology (2014) 170, 121–129 Introduction Decreased growth hormone (GH) secretion during aging, cognitive impairment, and reduced quality of life. Supple- hypogonadism, and obesity was recognized almost mentation of estradiol (E2) in girls or women and that of an four decades ago (1, 2, 3, 4). Low GH concentrations, in aromatizable androgen in boys or men stimulate GH turn, are associated with insulin resistance, dyslipidemia, production and alter the regularity of GH secretion patterns cardiovascular mortality, sarcopenia, osteopenia, possible (2, 3, 5). The importance of E2 is inferable in both sexes, www.eje-online.org Ñ 2014 European Society of Endocrinology Published by Bioscientifica Ltd. DOI: 10.1530/EJE-13-0733 Printed in Great Britain Downloaded from Bioscientifica.com at 09/27/2021 10:21:31PM via free access Clinical Study C Norman and others GHRP, GHRH, and SS in women 170:1 122 since an ER antagonist lowers GH concentrations in approved by the Mayo IRB. Screening consisted of medical women and men and an aromatase inhibitor blocks GH history, physical examination, and biochemical testing. responses to testosterone in men (2, 3, 6). Nonetheless, Eligibility required normal hepatic, renal, hematological, the precise clinical mechanisms mediating estrogen’s metabolic, and endocrine function and a negative augmentation of GH secretion remain largely unknown. mammogram within the last 12 months. Exclusion criteria The effects of gonadal estrogen on the GH axis have were hypopituitarism, hyperthyroidism, hyperprolactine- been investigated in animal models by ovariectomy mia, concurrent use of neuroactive medications or sex and transgenic silencing of the ERa (ESR1) and aromatase hormones, acute or chronic systemic illness, diabetes O genes (2,3,7).Inrats,E2 controls hypothalamic mellitus, weight loss ( 2 kg) in the last 3 months, systemic GH-releasing hormone (GHRH) neurons, hypothalamic inflammatory disease, BMI !20 or O32 kg/m2, greater receptors for GH-releasing peptide (GHRP), pituitary than three time-zone transmeridian travel in the last week, receptors for GHRH and GHRP, somatostatin (SS) receptor shift-work schedule, concurrent involvement in any other subtypes 2 and 5, and gastric ghrelin (native GHRP) study, drug or alcohol abuse, hemoglobin levels !2 g/dl, expression (2, 3, 7). The various effects of E2 on GHRH, thrombotic arterial disease (stroke, transient ischemic SS, and ghrelin secretion and action in animal models attack (TIA), myocardial infarction (MI), and angina), strongly suggest the estrogenic control of multiple peptide pulmonary embolism or thrombophlebitis, and history pathways. However, to date, available clinical studies of or suspicion of cancer or neoplasm (except for basal cell E2 action have evaluated primarily single-peptide effects, carcinoma if localized and treated surgically). rather than their interactions. To address this major limitation, the present study combined: i) experimental E2 treatment imposition of young-adult E2 concentrations in postme- nopausal women; ii) individual and combined infusions E2 supplementation was via daily transdermal E2 patches of hypothalamic peptides (GHRH, SS, and GHRP) for 13 h (Novartis) at escalating increasing doses, viz. 0.05 mg/day overnight; iii) deconvolution (secretion-based) and (184 nmol) for the first 4 days, 0.10 mg/day (368 nmol) for approximate entropy (ApEn, a pattern-regularity measure) the next 4 days, and 0.15 mg/day (552 nmol) for 20 analyses of GH concentration–time series; and iv) triple additional days (9). Overnight infusion studies were stimulation of GH secretion with L-arginine and initiated after at least 4 days on the highest (0.15 mg) E2 GHRH/GHRP to estimate maximal (pharmacological) dose. Medroxyprogesterone acetate (5 mg; Pharmacia and pituitary GH secretory capacity. The end points are Upjohn, New York, NY, USA) was given orally daily for European Journal of Endocrinology important, because burst-like (pulsatile) GH secretion 12 days after E2 supplementation, when all infusion/ and ApEn-quantified secretion regularity are physio- sampling sessions were completed. logically supervised modes of GH secretion (2, 3, 8). The postulate was that both the amount and pattern of GH Sampling schedule secretion are jointly specified by E2, GHRH, GHRP/ghrelin, and SS, along with BMI as a surrogate of relative adiposity. The participants were admitted to the CTSA by 1530 h on the evening of the study. To limit nutritional confounds, a standardized meal (33 kJ/kg of 50% carbohydrate, 20% Subjects and methods protein, and 30% fat) was served at 1600 h. The subjects then remained fasting, alcohol abstinent, and caffeine free Study design and volunteers until noon the next day. Vigorous exercise and daytime The study protocol was approved by the Mayo Institutional sleep were not allowed. Bilateral cannulas were placed in Review Board (IRB) and reviewed by the U.S. Food and Drug forearm veins at or before 1900 h to permit concurrent Administration. This was a double-blind, placebo- overnight blood sampling and peptide infusions. controlled, prospectively randomized study of 24 healthy, community-based, ambulatory women conducted in the Infusion and sampling paradigm Center for Translational Science Activities (CTSA). The subjects were healthy postmenopausal women (follicle- Each subject participated in a total of six (6) separate O stimulating hormone (FSH) levels 30 IU/l and E2 levels randomly ordered double-blind overnight consecutive !50 pmol/l) in the allowable age range of 50–80 years. The 13- and 3-h (total 16-h) infusion sessions (2000 h until subjects provided witnessed voluntary informed consent noon the next day) scheduled at least 48 h apart in the www.eje-online.org Downloaded from Bioscientifica.com at 09/27/2021 10:21:31PM via free access Clinical Study C Norman and others GHRP, GHRH, and SS in women 170:1 123 CTSA (Fig. 1). Three infusion sessions comprised continu- GHRH and GHRP2 (both i.v. at 1.0 mg/kg) at 0930 h. This ous i.v. saline infusions (30 ml/h) and the other three combination has been used by others (8). sessions comprised continuous i.v. GHRP2 infusions Blood (0.75 ml/sample) was withdrawn every 10 min (1 mg/kg per h) for 13 h (2000–0900 h). Based upon prior for 16 h (2000 h–noon) from all 24 subjects during all the dose–response curves obtained in older women (10, 11, six sessions. Sleep was not assessed in this study. Serum 12), bolus i.v. saline (Sal; 1 ml), GHRH (1.0 mg/kg), or SS that was separated was frozen at K70 8C until assay. (0.67 mg/kg) pulses were superimposed upon the continu- ous saline or GHRP2 infusions every 90 min for a total of Assays nine pulses during the inclusive time window 2000– 0850 h. GHRP2 was obtained from Kaken Pharmaceuticals GH concentrations were determined as a batch of 582 (Tokyo, Japan), and GHRH and SS were obtained from samples/subject via a robotics-assisted two-site monoclonal Bachem Laboratories (Torrance, CA, USA). immunoenzymatic chemiluminescence assay (sensitivity Immediately after the 13-h overnight pulsatile 0.010 mg/l). The assay standard was 22 kDa recombinant peptide infusions, a triple secretagogue was administered, human GH. Inter-assay coefficients of variation (CV) for GH followed by three more hours of sampling. This was done concentrations of 3.4 and 12 mg/l were 7.9 and 6.3% to test maximal (pharmacological) GH release. The triple respectively. Intra-assay CV values for GH concentrations stimulus comprised sequential i.v.
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