Characteristics and treatment responsiveness of patients with acromegaly and a paradoxical GH increase to oral glucose load.

OBJECTIVES: We aimed to investigate the clinical, biochemical, histological and radiological characteristics as well as the response to somatostatin analogs (SSA) in a large cohort of acromegaly patients with a paradoxical GH response (PR) to oral glucose tolerance test (OGTT). DESIGN: Retrospective study. METHODS: Of 110 patients with acromegaly included in our study, 30 (PR+; 27%) had a paradoxical GH increase of more than 25% relative to basal GH levels during OGTT. RESULTS: At diagnosis, PR+ patients were older than PR- patients (52 ± 16 years vs 44 ± 14 years, P < 0.05) and had smaller pituitary tumors (40% microadenomas vs 19%, P < 0.05), which were less often invasive (17% vs 35%, P < 0.05), overall more secreting (insulin-like growth factor-1 (IGF-1)/tumoral surface: 2.35 ULN/cm2 (0.28-9.06) vs 1.08 (0.17-7.87), P = 0.011), and more often hypointense on T2-weighted MRI (92% vs 48%, P = 0.001). While the rate of remission after surgery was similar in the two groups (69%), a better response to SSA treatment was observed in PR+ patients, either before (IGF-1 reduction of > 50% after 3-6 months in 77% vs 49%, P = 0.023) or after surgery (normalization of IGF-1 in 100% vs 44%, P = 0.011). CONCLUSIONS: Our study demonstrates that in acromegaly, a paradoxical GH increase during OGTT is associated with particular features of somatotroph adenomas and with a better prognosis in terms of response to SSA.

Clinical and hormonal findings in patients presenting with high IGF-1 and growth hormone suppression after oral glucose load: a retrospective cohort study.

OBJECTIVE: High insulin-like growth factor 1 (IGF-1) and unsuppressed growth hormone (GH) levels after glucose load confirm the diagnosis of acromegaly. Management of patients with conflicting results could be challenging. Our aim was to evaluate the clinical and hormonal evolution over a long follow-up in patients with high IGF-1 but normal GH nadir (GHn < 0.4 µg/L according to the latest guidelines). DESIGN: Retrospective cohort study. METHODS: We enrolled 53 patients presenting high IGF-1 and GHn < 0.4 µg/L, assessed because of clinical suspicion of acromegaly or in other endocrinological contexts (e.g. pituitary incidentaloma). Clinical and hormonal data collected at the first and last visit were analyzed. RESULTS: At the first evaluation, the mean age was 54.1 ± 15.4 years, 34/53 were females, median IGF-1 and GHn were +3.1 SDS and 0.06 µg/L, respectively. In the whole group, over a median time of 6 years, IGF-1 and GHn levels did not significantly change (IGF-1 mean of differences: -0.58, P = 0.15; GHn +0.03, P = 0.29). In patients with clinical features of acromegaly, the prevalence of acromegalic comorbidities was higher than in the others (median of 3 vs 1 comorbidities per patient, P = 0.005), especially malignancies (36% vs 6%, P = 0.03), and the clinical worsening overtime was more pronounced (4 vs 1 comorbidities at the last visit). CONCLUSIONS: In patients presenting high IGF-1 but GHn < 0.4 µg/L, a hormonal progression is improbable, likely excluding classical acromegaly in its early stage. However, despite persistently low GH nadir values, patients with acromegalic features present more acromegalic comorbidities whose rate increases over time. Close clinical surveillance of this group is advised.

Differential effects of androgens and estrogens over cellular GH sensitivity in HEPG2 cells.

Testosterone and estrogen concentrations progressively increase during puberty, and in association with growth hormone (GH), lead to the increase in height velocity known as the pubertal growth spurt. Very limited information is available however, regarding the possible effects of sex steroids over GH cellular sensitivity. OBJECTIVE: To investigate the effects of different concentrations of testosterone, estradiol and dihydrotestosterone over the GH intracellular signaling pathway. METHODS: We evaluated the effects of these sex steroids on the nuclear phosphorylation of STAT5b and IGF-1 expression, in HEPG2 human hepatoma cells. In addition, we studied whether Tamoxifen (TAM), can modulate these effects. RESULTS: The highest concentration of T tested (10 ng/mL) co-incubated with a fixed concentration of GH (40 ng/mL) increased nuclear STAT5b phosphorylation compared with GH alone (1.34 ± 0.2 vs 0.6 ± 0.09 AU; *p < 0.05), as well as IGF-1 expression (0.6 ± 0.03 vs 0.32 ± 0.05 AU; *p < 0.05). This effect was not observed with lower concentrations of T tested (1 and 5 ng/mL). A similar increase in nuclear STAT5b phosphorylation was observed with the lowest concentration of E2 tested (20 pg/mL), co-incubated with the same fixed concentration of GH (3.6 ± 0.5 vs 1.28 ± 0.33 AU; *p < 0.05). This effect was also associated with an increase in IGF-1 expression (0.73 ± 0.02 vs 0.39 ± 0.04 AU; *p < 0.05). These results were not observed with higher concentrations of E2 tested (75 and 200 pg/mL). DHT at concentrations of 0.1, 0.25 and 0.5 ng/mL, co-stimulated with GH, did not change cytoplasmic STAT5b phosphorylation, nuclear STAT5b or IGF-1 expression. In addition, the co-incubation of TAM with the highest concentration of T tested (10 ng/mL) and GH (40 ng/mL) did not change cytoplasmic, nuclear pSTAT5 levels or IGF-1 expression. CONCLUSIONS: T and E2 potentiate the GH signaling pathway in a concentration-dependent fashion. The observation that the non-aromatizable androgen dihydrotestosterone does not stimulate this pathway, and that the effects of T are blocked with TAM, suggests that the effects of T over the GH signaling pathway appear to be mediated by estrogen.

Multicenter, Observational Study of Lanreotide Autogel for the Treatment of Patients with Acromegaly in Routine Clinical Practice in Germany, Austria and Switzerland.

BACKGROUND: Evidence from controlled trials has shown that lanreotide autogel is effective in achieving biochemical and symptom control in patients with acromegaly. However, it is important to better understand the real-world patient population receiving lanreotide autogel treatment. METHODS: In this non-interventional study the long-term treatment response to lanreotide autogel in adult patients with acromegaly from office-based centers or clinics in Germany, Austria and Switzerland was studied. Assessments included growth hormone and insulin-like growth factor-I levels, symptoms, quality of life, lanreotide plasma levels and tumor somatostatin receptor subtype expression. The primary endpoint was achievement of full biochemical control, defined as growth hormone ≤2.5 µg/L and insulin-like growth factor I normalization at month 12. RESULTS: 76 patients were enrolled from 21 sites. 7/51 (13.7%) patients of the efficacy population had full biochemical control at baseline, 15/33 (45.5%) at month 12 and 10/26 (38.5%) at month 24 of treatment. At 12 months of treatment higher rates of biochemical control were observed in the following subgroups: older patients (>53 years [median]), females, treatment-naïve patients, and patients with a time since diagnosis of longer than 1.4 years (median). No clinically relevant differences in acromegaly symptoms or quality of life scores were observed. Median fasting blood glucose and glycated hemoglobin levels remained unchanged throughout the study. No new safety signals were observed. Overall tolerability of treatment with lanreotide autogel was judged by 80.8% of the enrolled patients at month 12 as 'very good' or 'good'. CONCLUSION: Treatment with lanreotide autogel in a real-world setting showed long-term effectiveness and good tolerability in patients with acromegaly.

Glucagon stimulation test to assess growth hormone status in Prader-Willi syndrome.

PURPOSE: Growth hormone deficiency (GHD) must be confirmed before starting treatment in adults with Prader-Willi syndrome (PWS). Most studies use the growth-hormone-releasing hormone plus arginine (GHRH-arginine) test. No data are available on the glucagon stimulation test (GST) in PWS. We compared the utility of fixed-dose (1 mg) GST versus GHRH-arginine test in diagnosing GHD. METHODS: Adults and late adolescents with PWS underwent both tests on separate days. In the GHRH-arginine test, GHD was defined according to body mass index. In the GST, two cutoffs were analyzed: peak GH concentration < 3 ng/mL and < 1 ng/mL. For analyses, patients were divided into two groups according to body weight (≤ 90 kg and > 90 kg). RESULTS: We analyzed 34 patients: 22 weighing ≤ 90 kg and 12 weighing > 90 kg. In patients weighing ≤ 90 kg, the two tests were concordant in 16 (72.72%) patients (k = 0.476, p = 0.009 with GST cutoff < 3 ng/mL, and k = 0.450, p = 0.035 with GST cutoff < 1 ng/mL). In patients weighing > 90 kg, the two tests were not concordant with GST cutoff < 3 ng/mL, but were concordant in 11 (91.6%) patients (k = 0.833, p = 0.003) with GST cutoff < 1 ng/mL. GH peaks on the two tests correlated (r = 0.725, p = 0.008). CONCLUSION: Fixed-dose (1 mg) GST using a peak GH cutoff of < 3 ng/mL or < 1 ng/mL promises to be useful for screening for GHD in adults and late adolescents with PWS. However, in those weighing > 90 kg, the < 1 ng/mL cutoff seems better. Larger studies are necessary to establish definitive glucagon doses and cutoffs, especially in extremely obese patients.

Clonidine GH stimulation test to differentiate MSA from idiopathic late onset cerebellar ataxia: a prospective, controlled study.

INTRODUCTION: Despite the consensus criteria for multiple system atrophy (MSA), the diagnosis of MSA of cerebellar type (MSA-C) may be difficult in the early stage of the disease. There are several differential diagnoses including idiopathic late-onset cerebellar ataxias (ILOCA) and it is often necessary to wait for clinical worsening so that the criteria can be met. Our aim was to assess the efficacy of clonidine growth hormone test (CGH test) to distinguish MSA-C from ILOCA in the early stage of the disease. METHODS: Within our cohort of late-onset sporadic, progressive cerebellar ataxia, the group of patients meeting the criteria for possible or probable MSA was compared to the ILOCA group. Clinical and paraclinical examination including CGH test were repeated during the prospective follow-up. RESULTS: Eighty-six patients were recruited, including 42 patients in the MSA group and 44 ILOCA patients with a mean follow-up of 33 months. At the inclusion visit, CHG test was pathological for 31% MSA of patients and 18.2% of ILOCA patients (p = 0.35). During the follow-up, 52.4% of MSA-C had a pathological CGH test, while only 20.5% of ILOCA (p < 0.01). CGH test had a sensitivity of 69.1% and a specificity of 68.2%, (p < 0.001) for MSA-C patients; CGH test allows in three quarters of cases, if negative, to rule out a probable MSA-C (negative predictive value of 75%, p = 0.0014). CONCLUSION: This prospective, controlled study showed that CGH test could be helpful in clinical practice to differentiate MSA-C from ILOCA in the early stage of the disease.

Interleukin-1α leads to growth hormone deficiency in adamantinomatous craniopharyngioma by targeting pericytes: implication in pituitary fibrosis.

BACKGROUND: The incidence of growth hormone deficiency (GHD) in adamantinomatous craniopharyngioma (aCP) is significantly higher than in other sellar region tumors, but the possible mechanism is still elusive. A high level of inflammatory responses is another feature of aCP. We investigated the internal connection between interleukin-1α (IL-1α) and GHD, while focusing on its biological activities in pituitary fibrosis. MATERIALS AND METHODS: To diagnosis of GHD, the Body Mass Index (BMI), Insulin Like Growth Factor-1(IGF-1) and peak growth hormone (GH) values after insulin stimulation test of 15 aCP patients were recorded. Histological staining was performed on the aCP samples. Levels of 9 proinflammatory cytokines in tumor tissue and cell supernatant were detected using Millipore bead arrays. The effect of IL-1α on GH secretion was evaluated in vivo and in vitro. Western blot, qRT-PCR and cell functional assays were used to explore the potential mechanism through which IL-1α acts on GH secretion. The stereotactic ALZET osmotic pump technique was used to simulate aCP secretion of proinflammatory cytokines in rats. Recombinant IL-1α (rrIL-1α) and conditioned media (CM) prepared from the supernatant of aCP cells was infused directly into the intra-sellar at a rate of 1 µl/h over 28 days, and then the effects of IL-1α treatment on pathological changes of pituitary gland and GH secretion were measured. To further confirm whether IL-1α affects GH secretion through IL-1R1, an IL-1R1 blocker (IL-1R1a, 10 mg/kg body weight, once daily) was administered subcutaneously from the first day until day 28. RESULTS: There was a significant positive correlation between pituitary fibrosis and GHD (rS = 0.756, P = 0.001). A number of cytokines, in particular IL-1α, interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1), were elevated in tumor tissue and cell supernatant. Only IL-1α showed a significant difference between the GHD group and the No-GHD group (P < 0.001, F = 6.251 in tumor tissue; P = 0.003, F = 1.529 in cell supernatant). IL-1α significantly reduced GH secretion in coculture of GH3 and pericytes. The activation of pericytes induced by IL-1α was mediated by the IL-1R1 signaling pathway. In vivo, IL-1α induces pituitary fibrosis, further leading to a decreased level of GH. This pathological change was antagonized by IL-1R1a. CONCLUSION: This study found that the cross talk between aCP cells and stroma cells in the pituitary, i.e. pericytes, is an essential factor in the formation of GHD, and we propose that neutralization of IL-1α signaling might be a potential therapy for GHD in aCP.

Effects of GLP-1 on counter-regulatory responses during hypoglycemia after GBP surgery.

OBJECTIVES: The aim of the study was to explore the role of GLP-1 receptor activation on the counter-regulation and symptoms of hypoglycemia in subjects who have undergone gastric bypass surgery (GBP). DESIGN: Experimental hyperinsulinemic-hypoglycemic clamp study. METHODS: Twelve post-GBP subjects participated in a randomized cross-over study with two hyperinsulinemic, hypoglycemic clamps (glucose nadir 2.7 mmol/L) performed on separate days with concomitant infusions of the GLP-1 analog exenatide or with saline, respectively. Continuous measurements of metabolites and counter-regulatory hormones as well as assessments of heart rate variability and symptoms of hypoglycemia were performed throughout the clamps. RESULTS: No effect of GLP-1 receptor activation on counter-regulatory hormones (glucagon, catecholamines, cortisol, GH) or glucose infusion rate was seen, but we found indications of a downregulation of the sympathetic relative to the parasympathetic nerve activity, as reflected in heart rate variability. No significant differences in symptom of hypoglycemia were observed. CONCLUSIONS/INTERPRETATION: Short-term exposure to a GLP-1 receptor agonist does not seem to impact the counter-regulatory hormonal and metabolic responses in post-GBP subjects during hypoglycemic conditions, suggesting that the improvement in symptomatic hypoglycemia post-GBP seen following treatment with GLP-1 receptor agonists may be mediated by mechanism not directly involved in counter-regulation.

Growth hormone (GH) receptor (GHR)-specific inhibition of GH-Induced signaling by soluble IGF-1 receptor (sol IGF-1R).

Human growth hormone (GH) binds and activates GH receptor (GHR) and prolactin (PRL) receptor (PRLR). LNCaP human prostate cancer cells express only GHR. A soluble fragment of IGF-1 receptor (IGF-1R) extracellular domain (sol IGF-1R) interacts with GHR and blocks GH signaling. We now explore sol IGF-1R's specificity for inhibiting GH signaling via GHR vs. PRLR and test GHR and PRLR extracellular domain inhibition determinants. Although T47D human breast cancer cells express GHR and PRLR, GH signaling is largely PRLR-mediated. In T47D, sol IGF-1R inhibited neither GH- nor PRL-induced STAT5 activation. However, sol IGF-1R inhibited GH-induced STAT5 activation in T47D-shPRLR cells, which harbor reduced PRLR. In MIN6 mouse ß-cells, bovine GH (bGH) activates mouse GHR, not PRLR, while human GH activates mouse GHR and PRLR. In MIN6, sol IGF-1R inhibited bGH-induced STAT5 activation, but partially inhibited human GH-induced STAT5 activation. These findings suggest sol IGF-1R's inhibition is GHR-specific. Using a cellular reconstitution system, we compared effects of sol IGF-1R on signaling through GHR, PRLR, or chimeras in which extracellular subdomains 2 (S2) of the receptors were swapped. Sol IGF-1R inhibited GH-induced STAT5 activation in GHR-expressing, not PRLR-expressing cells, consistent with GHR specificity of sol IGF-1R. Interestingly, we found that GHR S2 (which harbors the GHR-GHR dimer interface) was required, but not sufficient for sol IGF-1R inhibition of GHR signaling. These results suggest sol IGF-1R specifically inhibits GH-induced GHR-mediated signaling, possibly through interaction with GHR S1 and S2 domains. Our findings have implications for GH antagonist development.

Differences in multihormonal responses to the dopamine agonist apomorphine between unipolar and bipolar depressed patients.

BACKGROUND: A large number of studies suggest that dopaminergic function may be impaired in depressed patients, particularly in bipolar patients. The dopamine D2/D1 agonist apomorphine (APO) can be useful in the evaluation of dopaminergic function. However, most studies show conflicting results in APO test responses when evaluating unipolar and bipolar depressed patients. Thus, the objective of this study was to apply the APO test to assess whether hypothalamic-pituitary dopaminergic function is altered in unipolar and bipolar depression. METHODS: We evaluated multihormonal responses to APO test (0.75 mg subcutaneous) in 134 drug-free DSM-IV major depressed inpatients (54 with bipolar depression [BD] and 80 with unipolar depression [UD]), compared with 36 healthy controls (HCs). We also examined the cortisol response to the dexamethasone suppression test (DST, 1 mg orally) in all subjects. RESULTS: No significant differences in prolactin (PRL), cortisol, adrenocorticotropin (ACTH) or growth hormone (GH) baseline values were found across the three groups. ACTH/cortisol and GH responses to APO were also comparable. BD patients showed lower PRL suppression to APO than did UD patients and HCs (both p < 0.00001). Although responses to DST were comparable between UD and BD patients, the former exhibited higher post-DST cortisol levels than did HCs (p < 0.05). CONCLUSIONS: Our results suggest that BD patients, unlike UD patients, have altered post-synaptic D2 receptor sensitivity at the pituitary level. This alteration does not seem secondary to hypercortisolemia. These findings, if confirmed by other studies with larger samples, may support the use of dopamine agents in BD patients treatment.

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.

Sleep-endocrine effects of growth hormone-releasing hormone (GHRH) in patients with schizophrenia.

Changes in sleep-EEG after endocrine stimulation tests in patients with schizophrenia include reduced sleep efficiency, prolonged sleep latency and increased awaking after sleep onset Findings on sleep associated growth hormone (GH) secretion were ambiguous. The aim of this study was to elucidate the sleep-endocrine activity especially in the GH system of patients with schizophrenia after repeated administration of GHRH. The effect of repetitive injections of 4 × 50 µg GHRH between 22.00 and 01.00 h on sleep endocrine parameters was investigated in 9 patients diagnosed for schizophrenia. Patients did not receive any medication for one week. Concentrations of ACTH, cortisol, prolactin and GH were determined. Patients spent three consecutive nights in the sleep laboratory. Blood was taken every 20min. Results were compared with matched healthy controls. A non-significant prolonged sleep onset latency and increased time awake was found in patients compared to controls. Sleep stage 2 was significantly reduced in patients. No significant difference in ACTH and cortisol was detected, whereas the GH secretion in patients following GHRH stimulation was significantly elevated compared to controls. Our results in drug free patients confirm already known changes in sleep-EEG in these patients. The GH response to GHRH-stimulation indicates a different regulatory sensitivity of the system between daytime and night-time.

In Vitro Head-to-Head Comparison Between Octreotide and Pasireotide in GH-Secreting Pituitary Adenomas.

Context: First-generation somatostatin analogs (SSAs), such as octreotide (OCT), are the first line medical therapy for acromegaly. Pasireotide (PAS), a newly developed SSA, has shown promising results in the treatment of acromegaly. Objective: To compare the antisecretory effect of OCT and PAS in primary cultures of growth hormone (GH)-secreting pituitary adenomas (GH-omas). To correlate responses with the adenoma somatostatin receptor (SSTR) profile. Design: The effect of OCT and PAS on GH (and PRL) secretion was tested in 33 GH-oma cultures. SSTR expression was evaluated in adenoma samples. Setting and Patients: Patients with acromegaly referred to the Erasmus Medical Center (Rotterdam, The Netherlands). Interventions: OCT and PAS treatment for 72 hours (10 nM). Main Outcome Measures: GH (and PRL) concentrations in cell culture media. SSTR expression in adenoma samples. Results: The overall effect of OCT (-36.8%) and PAS (-37.1%) on GH secretion was superimposable. We identified three adenoma groups: PAS+ (PAS more effective than OCT), n = 6; PAS = OCT, n = 22; and OCT+ (OCT more effective than PAS), n = 5. PAS+ adenomas showed lower somatostatin receptor subtype (sst)2 messenger RNA (mRNA) and sst2/sst5 mRNA ratio, compared with the other groups (P < 0.05). PAS inhibited PRL hypersecretion more than OCT (P < 0.01). Conclusions: Overall, OCT and PAS equally reduced GH secretion in vitro. Adenomas with lower sst2 mRNA expression and lower sst2/sst5 mRNA ratio were better responders to PAS compared with OCT. SSTR evaluation in GH-omas may become a tool for tailored SSA treatment in acromegaly.

Protein supplementation does not alter intramuscular anabolic signaling or endocrine response after resistance exercise in trained men.

The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway appears to be the primary regulator of muscle protein synthesis. A variety of stimuli including resistance exercise, amino acids, and hormonal signals activate mTORC1 signaling. The purpose of this study was to investigate the effect of a protein supplement on mTORC1 signaling following a resistance exercise protocol designed to promote elevations in circulating hormone concentrations. We hypothesized that the protein supplement would augment the intramuscular anabolic signaling response. Ten resistance-trained men (age, 24.7 ± 3.4 years; weight, 90.1 ± 11.3 kg; height, 176.0 ± 4.9 cm) received either a placebo or a supplement containing 20 g protein, 6 g carbohydrates, and 1 g fat after high-volume, short-rest lower-body resistance exercise. Blood samples were obtained at baseline, immediately, 30 minutes, 1 hour, 2 hours, and 5 hours after exercise. Fine-needle muscle biopsies were completed at baseline, 1 hour, and 5 hours after exercise. Myoglobin, lactate dehydrogenase, and lactate concentrations were significantly elevated after resistance exercise (P < .0001); however, no differences were observed between trials. Resistance exercise also elicited a significant insulin, growth hormone, and cortisol response (P < .01); however, no differences were observed between trials for insulin-like growth factor-1, insulin, testosterone, growth hormone, or cortisol. Intramuscular anabolic signaling analysis revealed significant elevations in RPS6 phosphorylation after resistance exercise (P = .001); however, no differences were observed between trials for signaling proteins including Akt, mTOR, p70S6k, and RPS6. The endocrine response and phosphorylation status of signaling proteins within the mTORC1 pathway did not appear to be altered by ingestion of supplement after resistance exercise in resistance-trained men.

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.

GH signaling in human adipose and muscle tissue during 'feast and famine': amplification of exercise stimulation following fasting compared to glucose administration.

OBJECTIVE: Fasting and exercise stimulates, whereas glucose suppresses GH secretion, but it is uncertain how these conditions impact GH signaling in peripheral tissues. To test the original 'feast and famine hypothesis' by Rabinowitz and Zierler, according to which the metabolic effects of GH are predominant during fasting, we specifically hypothesized that fasting and exercise act in synergy to increase STAT-5b target gene expression. DESIGN AND METHODS: Eight healthy men were studied on two occasions in relation to a 1 h exercise bout: i) with a concomitant i.v. glucose infusion ('feast') and ii) after a 36 h fast ('famine'). Muscle and fat biopsy specimens were obtained before, immediately after, and 30 min after exercise. RESULTS: GH increased during exercise on both examination days and this effect was amplified by fasting, and free fatty acid (FFA) levels increased after fasting. STAT-5b phosphorylation increased similarly following exercise on both occasions. In adipose tissue, suppressors of cytokine signaling 1 (SOCS1) and SOCS2 were increased after exercise on the fasting day and both fasting and exercise increased cytokine inducible SH2-containing protein (CISH). In muscle, SOCS2 and CISH mRNA were persistently increased after fasting. Muscle SOCS1, SOCS3, and CISH mRNA expression increased, whereas SOCS2 decreased after exercise on both examination days. CONCLUSIONS: This study demonstrates that fasting and exercise act in tandem to amplify STAT-5b target gene expression (SOCS and CISH) in adipose and muscle tissue in accordance with the 'feast and famine hypothesis'; the adipose tissue signaling responses, which hitherto have not been scrutinized, may play a particular role in promoting FFA mobilization.

Unaltered ratio of circulating levels of growth hormone/GH isoforms in adults with Prader-Willi syndrome after GHRH plus arginine administration.

Human growth hormone (GH) is a heterogeneous protein hormone consisting of several isoforms, the most abundant being 22 kDa- and 20 kDa-GH. The availability of analytical methods to measure these GH isoforms might represent a valuable diagnostic tool to investigate GH hyposecretory states, including Prader-Willi syndrome (PWS), one of the most common causes of syndromic obesity. The aim of the present study was to measure circulating levels of 22 kDa- and 20 kDa-GH in PWS adults (n=14; M/F: 5/9; genotype DEL15/UPD15: 12/2; age: 19.0±3.7 years; BMI: 29.9±8.7 kg/m2) after combined GH releasing hormone (GHRH) plus arginine (ARG) administration. The results were analysed subdividing the study population in obese vs. nonobese (6/8) and GH deficient vs. nonGH deficient (GHD) (6/8) subjects, according to appropriate BMI-related diagnostic cut-off limits of GH peak response to the provocative test. Circulating levels of 22 kDa-GH were measured by a chemiluminescent method based on a detection monoclonal antibody targeting an epitope in the loop connecting helix 1 and 2 of GH, which is missing in 20 kDa-GH; the 20 kDa-GH was measured using a time resolved fluorescence assay based on two monoclonal antibodies with no cross-reactivity to 22-kDa GH. GHRH plus ARG significantly stimulated the secretions of 22 kDa- and 20 kDa-GH in nonobese (at 30, 45, 60 and 90 min and at 45, 60, 90 and 120 min vs. 0 min, p<0.05, with GH peaks of 15.8±10.3 ng/ml and 2.7±1.2 ng/ml, respectively) and in nonGHD PWS (at 30, 45 and 60 min and at 45, 60 and 90 min vs 0 min, p<0.05, with GH peaks of 12.5±9.0 ng/ml and 2.0±1.8 ng/ml, respectively). No significant GHRH plus ARG-induced changes in 22 kDa- and 20 kDa-GH were observed in obese or GHD PWS patients, the only exception being the increase of 22 kDa-GH (p<0.05) 60 min after the stimulus administration in GHD group (with GH peaks of 6.9±4.7 ng/ml and 0.8±0.6 ng/ml in obese subjects and 8.5±6.0 ng/ml and 1.2±1.0 ng/ml in GHD subjects for 22 kDa- and 20 kDa-GH, respectively). The GH responses for both isoforms were significantly higher in nonobese than in obese PWS patients (at 45 and 60 min for 22 kDa-GH and at 45, 60, 90 and 120 min for 20 kDa-GH, p<0.05), while no differences were detected between GHD vs. nonGHD groups. As previously reported in healthy subjects, the ratios of circulating levels of 22 kDa- to 20 kDa-GH remained constant after GHRH plus ARG both in obese/non-obese and GHD/non-GHD groups, thus suggesting the preservation of a normal balance in GH isoforms in PWS.

Effects of Antecedent GABA A Receptor Activation on Counterregulatory Responses to Exercise in Healthy Man.

The aim of this study was to determine whether antecedent stimulation of γ-aminobutyric acid (GABA) A receptors with the benzodiazepine alprazolam can blunt physiologic responses during next-day moderate (90 min) exercise in healthy man. Thirty-one healthy individuals (16 male/15 female aged 28 ± 1 year, BMI 23 ± 3 kg/m(2)) were studied during separate, 2-day protocols. Day 1 consisted of morning and afternoon 2-h hyperinsulinemic-euglycemic or hypoglycemic clamps with or without 1 mg alprazolam given 30 min before a clamp. Day 2 consisted of 90-min euglycemic cycling exercise at 50% VO2max. Despite similar euglycemia (5.3 ± 0.1 mmol/L) and insulinemia (46 ± 6 pmol/L) during day 2 exercise studies, GABA A activation with alprazolam during day 1 euglycemia resulted in significant blunting of plasma epinephrine, norepinephrine, glucagon, cortisol, and growth hormone responses. Lipolysis (glycerol, nonesterified fatty acids) and endogenous glucose production during exercise were also reduced, and glucose infusion rates were increased following prior euglycemia with alprazolam. Prior hypoglycemia with alprazolam resulted in further reduction of glucagon and cortisol responses during exercise. We conclude that prior activation of GABA A pathways can play a significant role in blunting key autonomous nervous system, neuroendocrine, and metabolic physiologic responses during next-day exercise in healthy man.

Potential risks of glucagon stimulation test in elderly people.

UNLABELLED: The glucagon stimulation test (GST) is a reliable measure for assessing growth hormone (GH) and adrenocorticotropic hormone (ACTH) secretion. The GST is considered to be a safe test, with few mild side effects, especially in adults and in the elderly in whom underlying co-morbidities may be present. OBJECTIVE: To describe the side effects of the GST in elderly people. DESIGN AND SETTING: The study was performed with patients of the geriatric ambulatory of our hospital who were recruited to voluntarily participate in a research study concerning the GH and ACTH axis in the elderly people. Forty-two subjects (n=5 males and 37 females) aged 67-88 years, without hypothalamic-pituitary disease, were submitted to the GST. The GST was performed by intramuscular injection of 1mg of glucagon. Blood samples were collected at baseline, and 90, 120, 150, and 180 min after glucagon injection for GH and cortisol measurements. RESULTS: During the test, 9 subjects (21.4%) had side effects, which included: nausea (14.2%), indisposition (11.9%), hypotension (9.5%), vomiting (7.1%), sweating (4.7%), and dizziness (2.3%). There were four cases of severe symptomatic hypotension, with inaudible blood pressure in two cases. In one case of severe hypotension, the subject suffered two episodes of generalized tonic seizures. Patients who had side effects at GST had statistically higher peak of cortisol (28.9 ± 6.67 µg/dL) and a statistical trend to higher GH peak (8.74 ± 5.96 µg/L). In the group of patients who did not have side effects, the mean cortisol and GH peak were 19.05 ± 5.36 µg/dL and 5.32 ± 3.52 µg/L, respectively. CONCLUSION: Although the GST is a reliable alternative test to the ITT, it should be cautiously used in the elderly because this population may have co-morbidities including vascular and cardiac diseases that could be potentiated with side effects of the test, such as severe hypotension.