Gender difference in the neuroendocrine regulation of growth hormone axis by selective estrogen receptor modulators

Role of Estrogen and Estrogen Receptor in GH-Secreting Adenomas

Acromegaly is a rare disease with several systemic complications that may lead to increased overall morbidity and mortality. Despite several available treatments, ranging from transsphenoidal resection of GH-producing adenomas to different medical therapies, complete hormonal control is not achieved in some cases. Some decades ago, estrogens were first used to treat acromegaly, resulting in a significant decrease in IGF1 levels. However, due to the consequent side effects of the high dose utilized, this treatment was later abandoned. The evidence that estrogens are able to blunt GH activity also derives from the evidence that women with GH deficiency taking oral estro-progestins pills need higher doses of GH replacement therapy. In recent years, the role of estrogens and Selective Estrogens Receptor Modulators (SERMs) in acromegaly treatment has been re-evaluated, especially considering poor control of the disease under first- and second-line medical treatment. In this review, we analyze the state of the art concerning the impact of estrogen and SERMs on the GH/IGF1 axis, focusing on molecular pathways and the possible implications for acromegaly treatment.

Sex difference in patients with controlled acromegaly-A multicentre survey

OBJECTIVE

Active acromegaly is subject to sex differences in growth hormone (GH) and Insulin like growth factor 1 (IGF-I) patterns as well as clinical features but whether this also pertains to controlled disease is unclear.

DESIGN

In a cross-sectional, multi-centre study, 84 patients with acromegaly (F = 43, M = 41), who were considered controlled after surgery alone (n = 23) or during continued somatostatin receptor ligand (SRL) treatment (n = 61), were examined.

METHODS

Serum concentrations of GH, insulin, glucose and free fatty acid (FFA) were measured during an oral glucose tolerance test (OGTT) together with baseline serum IGF-I and completion of two HR-Qol questionnaires (acromegaly quality of life questionnaire [AcroQol] and Patient-assessed Acromegaly Symptom Questionnaire [PASQ]).

RESULTS

The mean age at the time of the study was 57 (±1.1) years and the majority of females (were postmenopausal. Females had significantly higher fasting GH but comparable IGF-I standard deviation scores (SDS). Using fasting GH < 1.0 µg/L as cut off, disease control was less prevalent in females (F: 56% vs. M: 83%, p = .007) whereas a comparable figure was observed using IGF-I SDS < 2 (F:79% vs. M:76%, p = .71). Compared with males, female patients showed impaired AcroQol physical score (p = .05), higher fasting FFA (p = .03) and insulin concentrations during the OGTT (p = .04).

CONCLUSION

In patients with acromegaly considered controlled, postmenopausal females exhibited higher GH levels than males despite comparable IGF-I levels, which also translated into impaired metabolic health and well-being. Our findings point to the relevance of including GH measurements in the assessment of disease control and suggest that disease-specific sex differences prevail after treatment.

Disruption and recovery of testicular function during and after androgen abuse: the HAARLEM study

STUDY QUESTION

What is the speed and extent by which endogenous testosterone production and spermatogenesis recover after androgen abuse?

SUMMARY ANSWER

Testosterone concentrations normalized within 3 months after discontinuation of androgen abuse in most subjects but recovery of spermatogenesis took longer-approximately 1 year.

WHAT IS KNOWN ALREADY

An estimated 4-6% of amateur strength athletes use androgens. Abuse of supraphysiological doses of androgens completely suppresses endogenous testosterone production and spermatogenesis.

STUDY DESIGN, SIZE, DURATION

Prospective and observational cohort study in which 100 male amateur athletes participated for 1 year.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Subjects (≥18 years) were included if they had not used androgens for at least 3 months and intended to start an androgen cycle within 2 weeks. Clinic visits took place before (T0), at the end (T1), and 3 months after the end of the cycle (T2), and 1 year after start of the cycle (T3), and included a blood test for gonadotrophins and sex hormones, and semen analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

During androgen abuse, 77% of subjects had a total sperm count (TSC) below 40 million. Three months after the end of the cycle (T2), total (-1.9 nmol/l, CI -12.2 to 8.33, P = 0.71) and free (-38.6 pmol/l, CI -476 to 399, P = 0.86) testosterone concentrations were not different compared to baseline, whereas mean TSC was 61.7 million (CI 33.7 to 90.0; P < 0.01) lower than baseline. At the end of follow-up (T3), there was no statistically significant difference for total (-0.82 nmol/l, CI -11.5 to 9.86, P = 0.88) and free (-25.8 pmol/l, CI -480 to 428, P = 0.91) testosterone compared to baseline, but there was for TSC (-29.7 million, CI -59.1 to -0.39, P = 0.05). In nine (11%) subjects, however, testosterone concentrations were below normal at the end of follow-up (T3), and 25 (34%) subjects still had a TSC below 40 million.

LIMITATIONS, REASONS FOR CAUTION

The follow-up period (after the cycle) was relatively short, especially considering the long recovery time of spermatogenesis after discontinuation of androgens.

WIDER IMPLICATIONS OF THE FINDINGS

Endogenous testosterone production and spermatogenesis recover following androgen abuse in the vast majority of users. Nevertheless, not all users achieve a normalized testicular function. This may especially be the case for athletes with a high past exposure to androgens.

STUDY FUNDING/COMPETING INTEREST(S)

There is no conflict of interest. The study was funded by the Spaarne Gasthuis academy.

TRIAL REGISTRATION NUMBER

N/A.

Growth Hormone/Insulin Growth Factor Axis in Sex Steroid Associated Disorders and Related Cancers

To date, almost all solid malignancies have implicated insulin-like growth factor (IGF) signalling as a driver of tumour growth. However, the remarkable level of crosstalk between sex hormones, the IGF-1 receptor (IGF-1R) and its ligands IGF-1 and 2 in endocrine driven cancers is incompletely understood. Similar to the sex steroids, IGF signalling is essential in normal development as well as growth and tissue homoeostasis, and undergoes a steady decline with advancing age and increasing visceral adiposity. Interestingly, IGF-1 has been found to play a compensatory role for both estrogen receptor (ER) and androgen receptor (AR) by augmenting hormonal responses in the absence of, or where low levels of ligand are present. Furthermore, experimental, and epidemiological evidence supports a role for dysregulated IGF signalling in breast and prostate cancers. Insulin-like growth factor binding protein (IGFBP) molecules can regulate the bioavailability of IGF-1 and are frequently expressed in these hormonally regulated tissues. The link between age-related disease and the role of IGF-1 in the process of ageing and longevity has gained much attention over the last few decades, spurring the development of numerous IGF targeted therapies that have, to date, failed to deliver on their therapeutic potential. This review will provide an overview of the sexually dimorphic nature of IGF signalling in humans and how this is impacted by the reduction in sex steroids in mid-life. It will also explore the latest links with metabolic syndromes, hormonal imbalances associated with ageing and targeting of IGF signalling in endocrine-related tumour growth with an emphasis on post-menopausal breast cancer and the impact of the steroidal milieu.

The significance of estrogen receptors in acromegaly: Are they useful as predictors of prognosis and therapy regimen?

OBJECTIVE

In this study, we considered to assess the presence of estrogen receptors (ER) and the expression of estrogen receptor genes (ESR) in the surgical tissue samples of acromegaly patients and the control group patients with nonfunctioning adenoma and their association with disease activity. We also aimed to determine the significance of ER positivity in acromegaly patients and to find out whether it carries a potential to be used as a predictor of prognosis and therapy regimen in the future.

DESIGN

This study was conducted on a total of 67 patients over 18 years of age. The study group consisted of 34 patients with acromegaly and 33 patients with nonfunctioning pituitary adenoma. The pre- and post-operative basal pituitary hormone levels and magnetic resonance images (MRI) of all patients, as well as their remission status of all acromegaly patients were evaluated. Immunohistochemical (IHC) staining procedures for ER-α were performed on surgical tissue samples. Real-time quantitative polymerase chain reaction (RT-qPCR) method was used to determine the levels of ESR1 and ESR2 gene expressions.

RESULTS

We found that IHC staining for ER-α was positive in 31.3% and 45.5% of the patients with acromegaly and nonfunctioning adenoma respectively. There was no statistically significant difference of ER-α positivity, ER-α immunoreactivity score and ESR1/ESR2 gene expression levels among the study groups (p > .05). Nevertheless, the expression of ESR1 gene was found to be 0.26 times more, and the ESR2 gene to be 0.11 times less in the acromegaly group compared to those of the nonfunctioning adenoma group. Additionally, we detected the positivity of ER-α only in acromegaly patients who were in remission. An inverse association was found between the pre-operative insulin-like growth factor-1 (IGF-1) levels and the expressions of ESR1/ESR2 gene in acromegaly patients. So these results indicated that the high ESR1 and ESR2 gene expressions in acromegaly patients are associated to the decrease of pre-operative IGF-1 values. Also an inverse association was found between the pre-operative adenoma volume and ESR1 Ct values, means that increase in ESR1 gene expression is associated to the decrease of adenoma volume.

CONCLUSIONS

The current results may suggest the use of these parameters as useful prognostic markers because all ER-positive acromegaly patients were in remission and the high ESR1 and ESR2 gene expressions in acromegaly patients is associated to the decrease of pre-operative IGF-1 values. Our results need to be supported by further studies.

Anabolic androgenic steroid abuse in young males

This review summarizes 10 years experience with male abusers of anabolic androgenic steroids (AAS). The typical user of AAS is male, aged between 20 and 40 and lifting weights. Illegal AAS are cheap and easily obtained via internet or local suppliers. AAS are mostly used in cycles with a duration between 6 and 18 weeks. Most AAS cycles contain multiple agents, used simultaneously in a dose vastly exceeding a substitution dose. A variety of other performance and image-enhancing drugs are commonly used, including human growth hormone, thyroid hormone, tamoxifen, clomiphene citrate and human chorionic gonadotrophin. Short-term clinical and biochemical side effects are well established. Long-term side effects are uncertain, but may include heart failure, mood-and anxiety disorders, hypogonadism and subfertility. We share our views on the management of common health problems associated with AAS abuse.

Disparate Effect of Aromatization on the Central Regulation of GH Secretion by Estrogens in Men and Postmenopausal Women

CONTEXT

Estrogen receptor antagonism by tamoxifen inhibits GH secretion in both men and postmenopausal women, suggesting that estrogen, albeit at low concentration, stimulates GH secretion. However, systemic estrogen replacement in postmenopausal women does not enhance GH secretion. To clarify the role of estrogen in mediating GH secretion, we investigated the effect of estrogen deprivation by using aromatase inhibitors.

AIM

To determine whether estrogens mediate GH secretion in men and postmenopausal women.

DESIGN

The effects of letrozole, an aromatase inhibitor, and tamoxifen were compared in an open-label crossover study. Eight men and 14 women received tamoxifen (20 mg/d) and letrozole (2.5 mg/d) for 2 weeks each. The primary endpoints were GH response to arginine stimulation and gonadal steroid levels.

RESULTS

In men, letrozole significantly (P < 0.05) reduced the peak GH response to arginine (mean ± SEM; Δ -49.4% ± 18.1%). Tamoxifen also reduced the mean peak GH, but this did not reach statistical significance. In postmenopausal women, letrozole did not affect peak GH, whereas tamoxifen significantly (P < 0.05) reduced peak GH (Δ -47.3% ± 10%). In men, letrozole reduced circulating estradiol (from 43.1 ± 2.8 to 12.7 ± 1.3 pmol/L; P < 0.001), whereas in women estradiol was undetectable (<11 pmol/L) at baseline and throughout letrozole therapy.

CONCLUSION

Because estrogen deprivation reduced circulating GH, we conclude that estrogens regulate GH secretion in men. In postmenopausal women, the neutral effect of aromatase inhibition is likely explained by pre-existing estrogen deficiency. The inhibition of GH secretion by tamoxifen in menopause suggests a non-estrogen receptor-mediated mechanism of action. In contrast to men, estrogen is unlikely to mediate GH secretion in postmenopausal women.

Sex-Specific Associations of Androgen Receptor CAG Trinucleotide Repeat Length and of Raloxifene Treatment with Testosterone Levels and Perceived Stress in Schizophrenia

Lower testosterone levels are associated with greater negative symptoms in men with schizophrenia. Testosterone signals via androgen receptor (AR). A functional variant in the AR gene (CAG trinucleotide repeat polymorphism) is associated with circulating testosterone and mood-related symptoms in healthy people. Raloxifene increases testosterone in healthy males and reduces symptom severity and improves cognition in schizophrenia; however, whether raloxifene increases testosterone in men with schizophrenia is unknown. We assessed the interaction of a functional AR gene variant and adjunctive raloxifene on peripheral testosterone and symptom severity in schizophrenia. Patients with schizophrenia (59 males and 38 females) participated in a randomized, double-blind, placebo-controlled, crossover trial of adjunctive raloxifene (120 mg/day). Healthy adults (46 males and 41 females) were used for baseline comparison. Baseline circulating testosterone was decreased in male patients compared to male controls and positively correlated with CAG repeat length in male controls and female patients. Male patients with short, compared to long, CAG repeat length had higher stress scores. Raloxifene treatment increased testosterone in male patients, but was unrelated to AR CAG repeat length, suggesting that raloxifene's effects may not depend on AR activity. Sex-specific alterations of the relationship between AR CAG repeat length and testosterone suggest that altered AR activity may impact perceived stress in men with schizophrenia.

Effects of Toremifene, a Selective Estrogen Receptor Modulator, on Spontaneous and Stimulated GH Secretion, IGF-I, and IGF-Binding Proteins in Healthy Elderly Subjects

Context:

Estrogens amplify spontaneous and stimulated growth hormone (GH) secretion, whereas they diminish GH-dependent insulin-like growth factor (IGF)-I in a dose-dependent manner. Selective estrogen receptor modulators (SERMs), including tamoxifen and toremifene, are widely adjunctively used in breast and prostate cancer. Although some endocrine effects of tamoxifen are known, few data are available for toremifene.

Objective:

To explore sex-dependent effects of toremifene on spontaneous 10-hour overnight GH secretion, followed by GH-releasing hormone–ghrelin stimulation. Additionally, effects on IGF-I, its binding proteins, and sex hormone–binding globulin (SHBG) were quantified.

Participants and Design:

Twenty men and 20 women, within an allowable age range of 50 to 80 years, volunteered for this double-blind, placebo-controlled prospective crossover study. Ten-minute blood sampling was done for 10 hours overnight and then for 2 hours after combined GH-releasing hormone–ghrelin injection.

Main Outcome Measures:

Pulsatile GH and stimulated GH secretion, and fasting levels of IGF-I, IGF-binding protein (IGFBP)1, IGFBP3, and SHBG.

Results:

Toremifene did not enhance pulsatile or stimulated GH secretion, but decreased IGF-I by 20% in men and women. IGFBP3 was unchanged, whereas while IGFBP1 and SHBG increased in both sexes to a similar extent.

Conclusions:

The expected rise in spontaneous and stimulated GH secretion under the diminished negative feedback restraint of powered IGF-I favors a central inhibitory antiestrogenic effect of toremifene. Estrogenic effects of toremifene on the liver were present, as evidenced by increased IGFBP1 and SHBG levels. Men and women responded to this SERM comparably.

Sex steroids and the GH axis: Implications for the management of hypopituitarism

Growth hormone (GH) regulates somatic growth, substrate metabolism and body composition. Sex hormones exert profound effect on the secretion and action of GH. Estrogens stimulate the secretion of GH, but inhibit the action of GH on the liver, an effect that occurs when administered orally. Estrogens suppress GH receptor signaling by stimulating the expression proteins that inhibit cytokine receptor signaling. This effect of estrogens is avoided when physiological doses of estrogens are administered via a non-oral route. Estrogen-like compounds, such as selective estrogen receptor modulators, possess dual properties of inhibiting the secretion as well as the action of GH. In contrast, androgens stimulate GH secretion, driving IGF-1 production. In the periphery, androgens enhance the action of GH. The differential effects of estrogens and androgens influence the dose of GH replacement in patients with hypopituitarism on concomitant treatment with sex steroids. Where possible, a non-oral route of estrogen replacement is recommended for optimizing cost-benefit of GH replacement in women with GH deficiency. Adequate androgen replacement in conjunction with GH replacement is required to achieve the full anabolic effect in men with hypopituitarism.

Estrogens and selective estrogen receptor modulators in acromegaly

Despite recent advances in acromegaly treatment by surgery, drugs, and radiotherapy, hormonal control is still not achieved by some patients. The impairment of IGF-1 generation by estrogens in growth hormone deficient patients is well known. Patients on oral estrogens need higher growth hormone doses in order to achieve normal IGF-1 values. In the past, estrogens were one of the first drugs used to treat acromegaly. Nevertheless, due to the high doses used and the obvious side effects in male patients, this strategy was sidelined with the development of more specific drugs, as somatostatin receptor ligands and dopamine agonists. In the last 15 years, the antagonist of growth hormone receptor became available, making possible IGF-1 control of the majority of patients on this particular drug. However, due to its high cost, pegvisomant is still not available in many centers around the world. In this setting, the effect of estrogens and also of selective estrogen receptor modulators on IGF-1 control was reviewed, and proved to be an ancillary tool in the management of acromegaly. This review describes data concerning their efficacy and place in the treatment algorithm of acromegaly.

Biological factors and age-dependence of primary motor cortex experimental plasticity

To evaluate whether the age-dependence of brain plasticity correlates with the levels of proteins involved in hormone and brain functions we executed a paired associative stimulation (PAS) protocol and blood tests. We measured the PAS-induced plasticity in the primary motor cortex. Blood levels of the brain-derived neurotrophic factor (BDNF), estradiol, the insulin-like growth factor (IGF)-1, the insulin-like growth factor binding protein (IGFBP)-3, progesterone, sex hormone-binding globulin (SHBG), testosterone, and the transforming growth factor beta 1 (TGF-β1) were determined in 15 healthy men and 20 healthy women. We observed an age-related reduction of PAS-induced plasticity in females that it is not present in males. In females, PAS-induced plasticity displayed a correlation with testosterone (p = 0.006) that became a trend after the adjustment for the age effect (p = 0.078). In males, IGF-1 showed a nominally significant correlation with the PAS-induced plasticity (p = 0.043). In conclusion, we observed that hormone blood levels (testosterone in females and IGF-1 in males) may be involved in the age-dependence of brain plasticity.

Estrogen receptor antagonism uncovers gender-dimorphic suppression of whole body fat oxidation in humans: differential effects of tamoxifen on the GH and gonadal axes

CONTEXT

Tamoxifen, a selective estrogen receptor modulator, suppresses GH secretion in women but not in men. It increases testosterone levels in men. As GH and testosterone stimulate fat metabolism, the metabolic consequences of tamoxifen may be greater in women than in men.

OBJECTIVE

To determine whether tamoxifen suppresses fat oxidation (Fox) to a greater degree in women than in men.

DESIGN

An open-label study of ten healthy postmenopausal women and ten healthy men receiving 2-week treatment with tamoxifen (20  mg/day).

ENDPOINT MEASURES

GH response to arginine stimulation, serum levels of IGF1, testosterone and LH (men only), sex hormone binding globulin (SHBG) and whole body basal and postprandial Fox.

RESULTS

In women, tamoxifen significantly reduced the mean GH response to arginine stimulation (Δ -87%, P<0.05) and circulating IGF1 levels (Δ -23.5±5.4%, P<0.01). Tamoxifen reduced postprandial Fox in women (Δ -34.6±10.3%; P<0.05). In men, tamoxifen did not affect the GH response to arginine stimulation but significantly reduced mean IGF1 levels (Δ -24.8±6.1%, P<0.01). Tamoxifen increased mean testosterone levels (Δ 52±14.2%; P<0.01). Fox was not significantly affected by tamoxifen in men.

CONCLUSION

Tamoxifen attenuated the GH response to stimulation and reduced postprandial Fox in women but not in men. We conclude that at a therapeutic dose, the suppressive effect of tamoxifen on fat metabolism is gender-dependent. Higher testosterone levels may mitigate the suppression of GH secretion and Fox during tamoxifen treatment in men.

Localization of the aromatase enzyme expression in the human pituitary gland and its effect on growth hormone, prolactin, and thyroid stimulating hormone axis

The aim of this study is to evaluate aromatase expression in prolactin (PRL), thyroid stimulating hormone (TSH), and growth hormone (GH) secreting cells. Nontumoral human pituitary specimens were obtained from autopsy samples. Aromatase co-expression was determined by double immunohistochemical staining and assessed using H scores. H scores for GH-aromatase co-expression (GH-aromatase), TSH-aromatase co-expression (TSH-aromatase), and PRL-aromatase co-expression (PRL-aromatase) were 83.1 ± 13.1, 95.6 ± 16.1, and 83.7 ± 14.5, respectively. TSH producing cells exhibited the highest H score for co-expression of aromatase (p < 0.001). There was no gender difference in terms of H scores for aromatase expression and double immunohistochemical staining results (p > 0.05 for all). There was a negative correlation between the H scores for aromatase and PRL-aromatase, GH-aromatase and TSH-aromatase, respectively (r = -0.592, p < 0.001; r = -0.593, p < 0.001; r = -0.650, p < 0.001, respectively). Also, H scores for aromatase co-expression of each hormone were negatively correlated with the H scores for the corresponding hormone (r = -0.503, p < 0.001 for PRL-aromatase and PRL; r = -0.470, p < 0.001 for GH-aromatase, and GH; r = -0.641, p < 0.001 for TSH-aromatase and TSH). H scores for mean aromatase, GH-aromatase, TSH-aromatase were invariant of age (p > 0.05 for all). Age was negatively correlated with PRL-aromatase H score (r = -0.373, p = 0.008). Our study demonstrated significant aromatase co-expression in PRL, GH, and TSH secreting cells of the human anterior pituitary gland. The mutual paracrinal regulation between aromatase and three adenohypophyseal hormones indicates that aromatase may have a regulatory role on the synthesis and secretion of these hormones.

Aromatase enzyme expression in acromegaly and its possible relationship with disease prognosis

The purpose of this study was to evaluate aromatase enzyme expression in growth hormone (GH) secreting adenomas and comparison with prolactinomas, nonfunctional adenomas, and normal pituitary tissues. Also the impact of its expression on clinical and prognostic features was evaluated. 38 acromegaly, 26 prolactinoma, and 31 nonfunctional pituitary adenoma and 11 normal pituitary gland samples from autopsies were included. Aromatase and estrogen receptor-alpha (ERα) were evaluated by Immunohistochemical method; demographic, pre- and postoperative features of the patients were noted. Aromatase was expressed in varying degrees in all cases in study including controls. Aromatase expression in patients with acromegaly was significantly higher than patients with prolactinoma, nonfunctional adenoma, and controls (p = 0.04, p = 0.01 and p < 0.001, respectively). Taken together two functional adenoma groups, prolactinoma and acromegaly, aromatase expression was negatively correlated with ER-alpha (p = 0.02, r = -0.34). Also, Ki-67 immunohistochemical results were negatively correlated with aromatase expression (p = 0.03, r = -0.27) while positively correlated with ER expression (p < 0.01). Consistent with the growing evidence about testosterone effect on pituitary functions, aromatase expression was found to be higher in GH-secreting pituitary adenoma. Aromatase was expressed in all pituitary tissues including autopsy samples; however, it was highest in patients with acromegaly. In patients with acromegaly and prolactinoma, aromatase expression was negatively correlated with Ki-67 score, and also it was higher in patients with complete postoperative remission than without remission. Therefore, aromatase expression may be a good prognostic marker predominantly in acromegaly.

Neural growth hormone: regional regulation by estradiol and/or sex chromosome complement in male and female mice

BACKGROUND

Sex differences in pituitary growth hormone (GH) are well documented and coordinate maturation and growth. GH and its receptor are also produced in the brain where they may impact cognitive function and synaptic plasticity, and estradiol produces Gh sex differences in rat hippocampus. In mice, circulating estradiol increases Gh mRNA in female but not in male medial preoptic area (mPOA); therefore, additional factors regulate sexually dimorphic Gh expression in the brain. Thus, we hypothesized that sex chromosomes interact with estradiol to promote sex differences in GH. Here, we assessed the contributions of both estradiol and sex chromosome complement on Gh mRNA levels in three large brain regions: the hippocampus, hypothalamus, and cerebellum.

METHODS

We used the four core genotypes (FCG) mice, which uncouple effects of sex chromosomes and gonadal sex. The FCG model has a deletion of the sex-determining region on the Y chromosome (Sry) and transgenic insertion of Sry on an autosome. Adult FCG mice were gonadectomized and given either a blank Silastic implant or an implant containing 17β-estradiol. Significant differences in GH protein and mRNA were attributed to estradiol replacement, gonadal sex, sex chromosome complement, and their interactions, which were assessed by ANOVA and planned comparisons.

RESULTS

Estradiol increased Gh mRNA in the cerebellum and hippocampus, regardless of sex chromosome complement or gonadal sex. In contrast, in the hypothalamus, females had higher Gh mRNA than males, and XY females had more Gh mRNA than XY males and XX females. This same pattern was observed for GH protein. Because the differences in Gh mRNA in the hypothalamus did not replicate prior studies using other mouse models and tissue from mPOA or arcuate nucleus, we examined GH protein in the arcuate, a subdivision of the hypothalamus. Like the previous reports, and in contrast to the entire hypothalamus, a sex chromosome complement effect showed that XX mice had more GH than XY in the arcuate.

CONCLUSIONS

Sex chromosome complement regulates GH in some but not all brain areas, and within the hypothalamus, sex chromosomes have cell-specific actions on GH. Thus, sex chromosome complement and estradiol both contribute to GH sex differences in the brain.

Silvestre DH, Cavalcanti-de-Albuquerque JPA, Louzada RA, Carvalho DP, Werneck-de-Castro JP. Thyroid hormone and estrogen regulate exercise-induced growth hormone release

Growth hormone (GH) regulates whole body metabolism, and physical exercise is the most potent stimulus to induce its secretion in humans. The mechanisms underlying GH secretion after exercise remain to be defined. The aim of this study was to elucidate the role of estrogen and pituitary type 1 deiodinase (D1) activation on exercise-induced GH secretion. Ten days after bilateral ovariectomy, animals were submitted to 20 min of treadmill exercise at 75% of maximum aerobic capacity and tissues were harvested immediately or 30 min after exercise. Non-exercised animals were used as controls. A significant increase in D1 activity occurred immediately after exercise (~60%) in sham-operated animals and GH was higher (~6-fold) 30 min after exercise. Estrogen deficient rats exhibited basal levels of GH and D1 activity comparable to those found in control rats. However, after exercise both D1 activity and serum GH levels were blunted compared to sedentary rats. To understand the potential cause-effect of D1 activation in exercise-induced GH release, we pharmacologically blocked D1 activity by propylthiouracil (PTU) injection into intact rats and submitted them to the acute exercise session. D1 inhibition blocked exercise-induced GH secretion, although basal levels were unaltered. In conclusion, estrogen deficiency impairs the induction of thyroid hormone activating enzyme D1 in the pituitary, and GH release by acute exercise. Also, acute D1 activation is essential for exercise-induced GH response.

Discordance between growth hormone and insulin-like growth factor-1 after pituitary surgery for acromegaly: a stepwise approach and management

INTRODUCTION

Follow-up management of patients with acromegaly after pituitary surgery is performed by conducting biochemical assays of growth hormone (GH) and insulin-like growth factor-1 (IGF1). Despite concordant results of these two tests in the majority of cases, there is increasing recognition of patients who show persistent or intermittent discordance between GH and IGF1 (normal GH and elevated IGF1 or vice versa).

METHOD

In this narrative review, the last three decades materials on the issue of discrepancy between GH and IGF1 were thoroughly assessed.

RESULTS

Various studies have obtained different discordance rates, ranging from 5.4 to 39.5%. At present, despite the use of current sensitive assays and more stringent criteria to define remission, the rate of discordance still remains high. A number of mechanisms have been proposed to explain the postoperative discordance of GH and IGF1 including; altered dynamics of the GH secretion after surgery, early postoperative hormone assay, inaccurate or less sensitive tests and laboratory errors, too high cut-off point for GH suppression in the GH assays, GH nadir values not adjusted to age, sex, and body mass index, the influence of concomitant medication, co-existing physiologic and pathologic conditions, and many other proposed reasons. Nevertheless, the underlying mechanisms are still far from clear, and the solution continues to evade complete elucidation. Similarly, the impacts of such a discrepancy over mortality and morbidity and the risk of biochemical and/or clinical recurrence are unclear.

CONCLUSION

As a challenging clinical problem, a stepwise evaluation and management of these patients appears to be more rational.

Sex hormone-binding globulin gene expression and insulin resistance

CONTEXT

The plasma level of sex hormone binding globulin (SHBG), a glycoprotein produced by hepatocytes, is subject to genetic, hormonal, metabolic, and nutritional regulation, and is a marker for the development of the metabolic syndrome and diabetes.

OBJECTIVE

Because the mechanism for these associations is unclear, and no studies of SHBG gene expression in humans have been published, SHBG mRNA was measured in human liver samples and related to anthropometric data.

SETTING

Inpatients at a private, nonprofit, university-associated hospital were studied.

PARTICIPANTS

Subjects were fifty five adult men and women undergoing hepatic resection as treatment for cancer.

MAIN OUTCOME MEASURES

Main outcome measures were SHBG mRNA and serum SHBG levels.

RESULTS

SHBG mRNA was a strong predictor of serum SHBG with higher levels of the mRNA and protein in women than in men. The relationship between SHBG mRNA and circulating SHBG differed in males and females consistent with a sex difference in post-transcriptional regulation. A strong positive correlation was found between the level of the mRNA for the transcription factor HNF4α and SHBG mRNA. Insulin resistance (IR), assessed by homeostatis model assessment, was related inversely to SHBG mRNA and to HNF4α mRNA as well as to circulating SHBG levels. These mRNAs, as well as serum SHBG, were higher when the hepatic triglyceride concentration was low, and decreased with increasing body mass index but were unrelated to age.

CONCLUSIONS

Fat accumulation in liver and IR are important determinants of SHBG gene expression and thereby circulating SHBG levels that are perhaps mediated through effects on the transcription factor HNF4α. These findings provide a potential mechanism to explain why low SHBG predicts the development of type 2 diabetes.

Evaluation of Resettin® on serum hormone levels in sedentary males

Background

Comparisons of hormones such as dihydrotestosterone (DHT), estradiol (E2), and testosterone indicate their impact on metabolism and body composition. While less is known regarding DHT and E2, testosterone is an androgenic metabolic hormone capable of positively regulating a variety of anabolic and androgenic processes in the body. Accordingly, it has been postulated that the age-related reduction in serum testosterone levels leads to reductions in lean muscle mass, bone mineral density, and other physical conditions that impair physical performance and decrease quality of life. Preliminary studies suggest that key ingredients found in Resettin®/MyTosterone™, a natural supplement containing the carotenoid astaxanthin from Haematococcus pluvialis and Saw Palmetto berry lipid extract from Serenoa repens, could positively impact testosterone levels. To investigate the clinical efficacy of Resettin®, the serum profiles of testosterone, E2 and DHT in healthy sedentary males before and after Resettin® treatment were evaluated in a randomized, placebo controlled clinical trial.

Method

Twenty healthy, sedentary men between the ages of 21 and 70 were randomized into either an 800 mg/day or 1200 mg/day Resettin®/MyTosterone™ treatment group or lecithin, which was used as the placebo. After a 14-day treatment period, there was a 14-day washout period. After the wash-out period, participants were crossed over within their respective group to either Resettin®/MyTosterone™ or the lecithin placebo for 14 days.

Results

After 14 days, participants receiving 800 mg per day of Resettin® had significantly reduced baseline-subtracted serum DHT levels in comparison to the placebo control group. While after 14 days, participants receiving 1200 mg per day of Resettin® had significantly reduced baseline-subtracted serum DHT and E2 levels in comparison to the placebo control group. Moreover, participants receiving 1200 mg per day of Resettin® experienced a 38% increase in serum testosterone levels in comparison to the placebo control group, but the effect did not reach statistical significance.

Conclusion

Although additional studies will be required to evaluate how Resettin® may promote proper testosterone regulation, these findings indicate that Resettin® can favorably influence serum hormone profiles in men.

Estrogen and selective estrogen receptor modulators (SERMs) for the treatment of acromegaly: a meta-analysis of published observational studies

Estrogen and selective estrogen receptor modulator (SERM) treatments for acromegaly have received limited attention since the development of newer pharmacologic therapies. There has been ongoing research evidence suggesting their utility in the biochemical control of acromegaly. Therefore, the aim of this meta-analysis was to synthesise current evidence with a view to determining to what extent and in which acromegalic patient subsets do estrogen and SERMs reduce IGF-1 levels. A literature search was conducted (finished December 2012), which included all studies pertaining to estrogen or SERM treatment and IGF-1. Seven patient subsets were identified from six published observational studies, and were pooled using meta-analytic methods. Overall, the pooled mean loss in IGF-1 was -29.09 nmol/L (95 % CI -37.23 to -20.95). A sensitivity analysis indicated that women receiving estrogen had a substantially greater reduction in IGF-1 levels compared with women receiving SERMs, with a weighted mean loss in IGF-1 of -38.12 nmol/L (95 % CI -46.78 to -29.45) compared with -22.91 nmol/L (95 % CI -32.73 to -13.09). There was a trend that did not reach statistical significance for men receiving SERM treatment at -11.41 nmol/L (95 % CI -30.14 to 7.31). It was concluded that estrogen and SERMs are a low cost and effective treatment to achieve control of IGF-1 levels in acromegalic women either as concomitant treatment for refractory disease, or where access to conventional therapy is restricted. Their use in men requires further study.

Raloxifene activates G protein-coupled estrogen receptor 1/Akt signaling to protect dopamine neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice

Raloxifene, used in the clinic, is reported to protect brain dopaminergic neurons in mice. Raloxifene was shown to mediate an effect through the G protein-coupled estrogen receptor 1 (GPER1). We investigated if raloxifene neuroprotective effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated male mice is mediated through GPER1 by using its antagonist G15. Striatal concentrations of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid to dopamine ratio as well as dopamine transporter and vesicular monoamine transporter 2 showed that raloxifene neuroprotection of dopaminergic neurons was blocked by G15. Protection by raloxifene was accompanied by activation of striatal Akt signaling (but not ERK1/2 signaling) and increased Bcl-2 and brain-derived neurotrophic factor levels; these effects were abolished by coadministration with G15. The effect of raloxifene was not mediated through increased levels of 17β-estradiol. MPTP mice had decreased plasma testosterone, dihydrotestosterone, and 3β-diol levels; this was prevented in raloxifene-treated MPTP mice. Our results suggest that raloxifene acted through GPER1 to mediate Akt activation, increase Bcl-2 and brain-derived neurotrophic factor levels, and protection of dopaminergic neurons and plasma androgens.

A long-acting human growth hormone with delayed clearance (VRS-317): results of a double-blind, placebo-controlled, single ascending dose study in growth hormone-deficient adults

BACKGROUND

Administration of daily recombinant human GH (rhGH) poses a considerable challenge to patient compliance. Reduced dosing frequency may improve treatment adherence and potentially overall treatment outcomes.

OBJECTIVES

This study assessed the safety and tolerability and the potential for achieving IGF-I levels within the target range in adults with GH deficiency after a single dose of the long-acting rhGH analog, VRS-317.

DESIGN

This was a randomized, double-blind, placebo-controlled, single ascending dose study.

PATIENTS

Fifty adults with growth hormone deficiency (mean age, 45 years) were studied in 5 treatment groups of 10 subjects each (8 active drug and 2 placebo).

SETTING

The study was conducted in 17 adult endocrinology centers in North America and Europe.

MAIN OUTCOME MEASURES

Adverse events, laboratory safety assessments, and VRS-317 pharmacokinetics and pharmacodynamics (IGF-I and IGF binding protein-3) were analyzed.

RESULTS

At 0.80 mg/kg, VRS-317 had a mean terminal elimination half-life of 131 hours. Single VRS-317 doses of 0.05, 0.10, 0.20, 0.40, and 0.80 mg/kg (approximately equivalent to daily rhGH doses of 0.3-5.0 μg/kg over 30 d) safely increased the amplitude and duration of IGF-I responses in a dose-dependent manner. After a single 0.80 mg/kg dose, serum IGF-I was maintained in the normal range between -1.5 and 1.5 SD values for a mean of 3 weeks. No unexpected or serious adverse events were observed.

CONCLUSIONS

The elimination half-life for VRS-317 is 30- to 60-fold longer and stimulates more durable IGF-I responses than previously studied rhGH products. Prolonged IGF-I responses do not come at the expense of overexposure to high IGF-I levels. The pharmacokinetics and pharmacodynamics combined with the observed safety profile indicate the potential for safe and effective monthly dosing.