hGH Secretion Research Articles

Acromegaly: The Impacts of HGH Release on Patient Progression

Hypersecretion of human Growth Hormone (hGH) is the primary mechanism driving Acromegaly, a disease characterised by abnormal growth of extremities and disfigured facial features. This article will discuss hGH secretion, its effect on Acromegaly, and potential treatments for the disease, among other key topics.

In silico and in vitro analysis of a rational mutation in gIII signal peptide and its effects on periplasmic expression of rhGH in E. coli

The secretion efficiency of a heterologous protein in E. coli is mainly dictated by the N-terminal signal peptide fused to the desired protein. In this study, we aimed to select and introduce mutations into the – 1, – 2 and – 3 positions of the gIII signal peptide (originated from filamentous phage fd Gene III) fused to the N-terminus of the human growth hormone (hGH), and study its effect on the secretion efficiency of the recombinant hGH into the periplasmic space of E. coli Top10. Bioinformatics software such as SignalP-5.0 and PrediSi were employed to predict the effects of the mutations on the secretion efficiency of the recombinant hGH. Site-directed mutagenesis was applied to introduce the desired mutations into the C-terminus of the gIII signal peptide. The periplasmic expression and the secretion efficiency of the recombinant hGH using the native and mutant gIII signal peptides were compared in E. coli Top10 under the control of araBAD promoter. Our results from bioinformatics analysis indicated that the mutant gIII signal peptide was more potent than the native one for secretion of the recombinant hGH in E. coli. While our experimental results revealed that the mutation had no effect on hGH secretion. This result points to the importance of experimental validation of bioinformatics predictions.

Optimization of expression, purification and secretion of functional recombinant human growth hormone in Escherichia coli using modified staphylococcal protein a signal peptide

BackgroundHuman Growth Hormone (hGH) is a glycoprotein released from the pituitary gland. Due to the wide range of effects in humans, any disruption in hGH secretion could have serious consequences. This highlights the clinical importance of hGH production in the treatment of different diseases associated with a deficiency of this hormone. The production of recombinant mature hormone in suitable hosts and secretion of this therapeutic protein into the extracellular space can be considered as one of the best cost-effective approaches not only to obtain the active form of the protein but also endotoxin-free preparation. Since the natural growth hormone signal peptide is of eukaryotic origin and is not detectable by any of the Escherichia coli secretory systems, including Sec and Tat, and is therefore unable to secrete hGH in the prokaryotic systems, designing a new and efficient signal peptide is essential to direct hGh to the extracellular space.ResultsIn this study, using a combination of the bioinformatics design and molecular genetics, the protein A signal peptide from Staphylococcus aureus was modified, redesigned and then fused to the mature hGH coding region. The recombinant hGH was then expressed in E. coli and successfully secreted to the medium through the Sec pathway. Secretion of the hGH into the medium was verified using SDS-PAGE and western blot analysis. Recombinant hGH was then expressed in E. coli and successfully secreted into cell culture medium via the Sec pathway. The secretion of hGH into the extracellular medium was confirmed by SDS-PAGE and Western blot analysis. Furthermore, the addition of glycine was shown to improve hGH secretion onto the culture medium. Equations for determining the optimal conditions were also determined. Functional hGH analysis using an ELISA-based method confirmed that the ratio of the active form of secreted hGH to the inactive form in the periplasm is higher than this ratio in the cytoplasm.ConclusionsSince the native signal protein peptide of S. aureus protein A was not able to deliver hGH to the extracellular space, it was modified using bioinformatics tools and fused to the n-terminal region of hGh to show that the redesigned signal peptide was functional.

Sleep deprivation and diet affect human GH gene expression in transgenic mice in vivo.

Human (h) growth hormone (GH) production studies are largely limited to effects on secretion. How pituitary hGH gene (hGH-N/GH1) expression is regulated is important in our understanding of the role hGH plays in physiology and disease. Here we assess for the first time the effect of sleep deprivation (SD) and high-fat diet (HFD) on hGH-N expression in vivo using partially humanized 171hGH/CS transgenic (TG) mice, and attempted to elucidate a role for DNA methylation. Activation of hGH-N expression requires interactions between promoter and upstream locus control region (LCR) sequences including pituitary-specific hypersensitive site (HS) I/II. Both SD and diet affect hGH secretion, but the effect of SD on hGH-N expression is unknown. Mice fed a HFD or regular chow diet for 3 days underwent SD (or no SD) for 6 h at Zeitgeber time (ZT) 3. Serum and pituitaries were assessed over 24 h at 6-h intervals beginning at ZT 14. SD and HFD caused significant changes in serum corticosterone and insulin, as well as hGH and circadian clock-related gene RNA levels. No clear association between DNA methylation and the negative effects of SD or diet on hGH RNA levels was observed. However, a correlation with increased methylation at a CpG (cytosine paired with a guanine) in a putative E-box within the hGH LCR HS II was suggested in situ. Methylation at this site also increased BMAL1/CLOCK-related nuclear protein binding in vitro. These observations support an effect of SD on hGH synthesis at the level of gene expression.

Mechanism for the Increase in Human Growth Hormone with Administration of a Novel Test Supplement and Results Indicating Improved Physical Fitness and Sleep Efficiency.

An oral test supplement increases serum human growth hormone (hGH) levels after acute administration in healthy adults. We investigated the mechanism for the increase in hGH and the effect of continued daily administration of the test supplement on measures of physical fitness and sleep efficiency. In Study 1, serum triiodothyronine (T3) was measured in samples from a prior placebo-controlled, double-blind study in which 16 healthy participants received both placebo and the test supplement in a crossover design; treatment order was randomized, and treatments were separated by a 1-week washout. In Study 2, physical fitness (VO2 max) was measured at baseline and after 2 weeks of daily administration of the test supplement (N = 12 healthy participants). Study 3 assessed daily sleep onset latency and time awake during 3 weeks of daily administration of the test supplement (N = 15 healthy participants). A fall from baseline in T3 was observed with placebo (-6.1 ± 8.5 ng/dL, P = .01). Of note, the change in T3 was smaller with the test supplement (-3.3 ± 10.7 ng/dL, P = not significant) but was not statistically different from placebo. Mean VO2 max increased by 6% from baseline after 2 weeks (P = .02). Sleep-onset latency and time awake during the night were reduced from baseline to week 3 by 22% and 65%, respectively (P = .01 and P = .02). The conservation of T3 levels suggests that the mechanism for increased hGH secretion by the test supplement is through somatostatin inhibition. Furthermore, pilot studies indicated that daily administration of the supplement improved physical fitness and sleep efficiency from baseline, effects consistent with increased endogenous hGH release. Clinical Trial Registration No. NCT02987868.

MON-LB003 Clinical Case Series of Augmented Fertility in Females After Administration of an Amino Acid Blend That Enhances Release of Human Growth Hormone

Supplementation with adjuvant therapies, including growth hormone (hGH), is commonly used to improve fertility treatment outcomes. hGH is important for normal female fertility; low hGH has been associated with causes of infertility and impaired fertility, including polycystic ovarian syndrome (PCOS), endometriosis, diminished ovarian reserve (DOR), and advanced maternal age. A novel, low dose, orally administered amino acid blend has been previously shown in a double-blind, randomized, placebo-controlled, crossover clinical trial to produce a statistically significant increase in endogenous hGH secretion. In this clinical case series, we report outcomes in 7 women with infertility or impaired fertility and conditions associated with low hGH who administered the amino acid blend during fertility treatment (n=5) or timed intercourse/spontaneous pregnancy (n=2). Medical history included conditions associated with impaired fertility and low hGH: endometriosis (n=3), PCOS (n=2), and poor response to ovarian stimulation/history of failed in vitro fertilization (IVF) (n=3). The amino acid blend (containing 2.9 g of L-lysine, L-arginine, oxo-proline, N-acetyl-L-cysteine, L-glutamine, and schizonepeta) was administered daily on an empty stomach. Outcomes included embryo quality and success of embryo transfer (for IVF) and successful pregnancy/live births. Mean±SD age was 33±5 years (range 27-38) and BMI was 27±7 kg/m2 (range 21-37). Time to pregnancy ranged from 1 week to 9 months (median 3 months) prior to egg retrieval for IVF (n=4), intrauterine insemination (n=1), or timed intercourse/spontaneous pregnancy (n=2). For women with a history of failed IVF (n=3), there was an improvement in oocyte retrieval, a higher fertilization rate, and a greater number of high-quality embryos compared to previous IVF attempts. There were 2 twin pregnancies (both following IVF). All 7 pregnancies resulted in live births. Consistent with previous studies, the amino acid blend was well tolerated; no adverse events were observed. We report a case series of successful pregnancy in 7 women with conditions associated with low hGH including PCOS, endometriosis, and poor response to ovarian stimulation/history of failed IVF who administered the amino acid blend concomitant with fertility treatment or who reported spontaneous pregnancy. This may represent a potential low-risk and cost-effective treatment to improve IVF success and increase pregnancy rates in individuals with infertility or impaired fertility.

SUN-439 Improvement in Insulin-Like Growth Factor-1 and Clinical Symptoms: Results of an Open-Label, Single-Arm Study of a Human Growth Hormone-Enhancing Amino Acid Supplement

SeroVital is an orally-administered amino acid supplement that promotes hGH secretion via suppression of somatostatin. We investigated if daily administration of the supplement would increase levels of endogenous insulin-like growth factor 1 (IGF-1), a primary mediator of the effects of hGH, and improve symptoms related to low-normal hGH production in a cohort of individuals being treated for fibromyalgia, a complicated condition associated with endocrine features including low or low-normal hGH. This open-label, single-arm study investigated the effects of 24 weeks of daily oral administration of the supplement in individuals with low-normal hGH production (between the 15th and 50th percentile for age-appropriate levels of IGF-1). The primary endpoint was the change from baseline to endpoint (Week 24) in serum IGF-1. Additional endpoints included the change in body weight, clinical symptoms (assessed with the Revised Fibromyalgia Impact Questionnaire [FIQR], range 0-100, and Perceived Stress Scale [PSS], range 0-40), fasting cardiometabolic markers, tolerability, and safety. Participants continued to receive standard care. The study enrolled 45 adults with mean baseline age (mean±SD) 67±11 years, 67% female, BMI 31±7 kg/m2, and IGF-1 107±28 ng/mL. High mean±SD baseline FIQR and PSS scores of 82±14 and 35±3, respectively, indicated poor to moderate control of fibromyalgia with standard care. All individuals completed 24 weeks of treatment. There was an increase in serum IGF-1 levels at Week 12 that was sustained to endpoint, resulting in a mean±SE Week 24 change of 32.1±2.8 ng/mL (paired t-test p<0.001). IGF binding protein-3 (IGFBP-3) levels were unchanged from baseline (p=ns), indicating no change in IGF-1 sensitivity. There was a steady reduction in body weight that resulted in Week 24 mean±SE change of -6.4±0.4 kg (p<0.001). The change from baseline in FIQR and PSS scores were -25.6±1.6 and -21.5±0.5, respectively (both p<0.001), indicating a substantial improvement. Statistically significant improvements from baseline were also observed for systolic and diastolic blood pressure, HbA1c, LDL and HDL cholesterol, and triglycerides (all p<0.001). The supplement was well tolerated; no adverse events were reported. In patients being treated for fibromyalgia with low-normal hGH production, daily addition of the hGH-enhancing supplement for 24 weeks produced an increase in IGF-1 with associated weight loss and improvements in cardiometabolic markers and clinical symptoms. Sustained augmentation of IGF-1 with the supplement may represent a unique method of improving clinical symptoms in individuals with low-normal hGH, including otherwise healthy adults exhibiting low-normal hGH production.This was an independent investigator-initiated study. Sierra Research Group provided some samples of the supplement.

Designing Signal Peptides for Efficient Periplasmic Expression of Human Growth Hormone in Escherichia coli.

The secretion efficiency of a protein in a Sec-type secretion system is mainly determined by an N-terminal signal peptide and its combination with its cognate protein. Five signal peptides, namely, two synthetic Sec-type and three Bacillus licheniformis alpha-amylase-derived signal peptides, were compared for periplasmic expression of the human growth hormone (hGH) in E. coli. Based on in silico predictions on the signal peptides' cleavage efficiencies and their corresponding mRNA secondary structures, a number of amino acid substitutions and silent mutations were considered in the modified signal sequences. The two synthetic signal peptides, specifically designed for hGH secretion in E. coli, differ in their N-terminal positively charged residues and hydrophobic region lengths. According to the mRNA secondary structure predictions, combinations of the protein and each of the five signal sequences could lead to different outcomes, especially when accessibility of the initiator ATG and ribosome binding sites were considered. In the experimental stage, the two synthetic signal peptides displayed complete processing and resulted in efficient secretion of the mature hGH in periplasmic regions, as was demonstrated by protein analysis. The three alpha-amylase-derived signal peptides, however, were processed partially from their precursors. Therefore, to achieve efficient secretion of a protein in a heterologous system, designing a specific signal peptide by using a combined approach of optimizations of the mRNA secondary structure and the signal peptide H-domain and cleavage site is recommended.

In Silico Evaluation of Different Signal Peptides for the Secretory Production of Human Growth Hormone in E. coli

Various advantages of protein secretion have prompted scientists to search for secretory production of heterologous proteins. Signal peptides are one of the most important factors for prosperous secretion of the recombinant proteins. The aim of this study was to evaluate 23 different signal peptides and theoretically determine suitable ones for secretory production of the human growth hormone (hGH) in the E. coli host. The signal peptide sequences and the precise location of their cleavage sites were predicted using SignalP 4.0 server. Accordingly, six of the signal peptides, including hGH, major outer membrane lipoprotein, protease VII, protein TolB, periplasmic protein TorT and beta-lactamase TEM were excluded from the further study, due to their inappropriate cleavage scores. Different physico-chemical properties, which are essential for selecting a proper signal peptide, were evaluated using ProtParam and Solpro as the most accurate and reliable servers. Computational analysis of the above-mentioned factors, indicates that outer membrane protein C, fimbrial chaperone SfmC, outer membrane protein F and disulfide interchange protein DsbA can theoretically be suitable signal peptides for hGH secretion.

Butyrate increases intracellular calcium levels and enhances growth hormone release from rat anterior pituitary cells via the G-protein-coupled receptors GPR41 and 43.

Butyrate is a short-chain fatty acid (SCFA) closely related to the ketone body ß-hydroxybutyrate (BHB), which is considered to be the major energy substrate during prolonged exercise or starvation. During fasting, serum growth hormone (GH) rises concomitantly with the accumulation of BHB and butyrate. Interactions between GH, ketone bodies and SCFA during the metabolic adaptation to fasting have been poorly investigated to date. In this study, we examined the effect of butyrate, an endogenous agonist for the two G-protein-coupled receptors (GPCR), GPR41 and 43, on non-stimulated and GH-releasing hormone (GHRH)-stimulated hGH secretion. Furthermore, we investigated the potential role of GPR41 and 43 on the generation of butyrate-induced intracellular Ca2+ signal and its ultimate impact on hGH secretion. To study this, wt-hGH was transfected into a rat pituitary tumour cell line stably expressing the human GHRH receptor. Treatment with butyrate promoted hGH synthesis and improved basal and GHRH-induced hGH-secretion. By acting through GPR41 and 43, butyrate enhanced intracellular free cytosolic Ca2+. Gene-specific silencing of these receptors led to a partial inhibition of the butyrate-induced intracellular Ca2+ rise resulting in a decrease of hGH secretion. This study suggests that butyrate is a metabolic intermediary, which contributes to the secretion and, therefore, to the metabolic actions of GH during fasting.

Toward gene therapy for growth hormone deficiency via salivary gland expression of growth hormone

Salivary glands are useful targets for gene therapeutics. After gene transfer into salivary glands, regulated secretory pathway proteins, such as human growth hormone, are secreted into saliva, whereas constitutive secretory pathway proteins, such as erythropoietin, are secreted into the bloodstream. Secretion of human growth hormone (hGH) into the saliva is not therapeutically useful. In this study, we attempted to redirect the secretion of transgenic hGH from the saliva to the serum by site-directed mutagenesis. We tested hGH mutants first in vitro with AtT20 cells, a model endocrine cell line that exhibits polarized secretion of regulated secretory pathway proteins. Selected mutants were further studied in vivo using adenoviral-mediated gene transfer to rat submandibular glands. We identified two mutants with differences in secretion behavior compared to wild-type hGH. One mutant, ΔN1-6 , was detected in the serum of transduced rats, demonstrating that expression of this mutant in the salivary gland resulted in its secretion through the constitutive secretory pathway. This study demonstrates that mutagenesis of therapeutic proteins normally destined for the regulated secretory pathway may result in their secretion via the constitutive secretory pathway into the circulation for potential therapeutic benefit.

Ghrelin Stimulation of Growth Hormone Isoforms: Parallel Secretion of Total and 20-kDa Growth Hormone and Relation to Insulin Sensitivity in Healthy Humans

The 20-kDa human GH (hGH) is produced in the pituitary by alternative splicing of the hGH-N gene. The 20-kDa hGH promotes growth similarly to 22-kDa or total hGH, the predominant form in circulation, but the relative effects of these isoforms on glucose metabolism have been debated. To investigate the effect of ghrelin on 20-kDa and total hGH secretion in healthy, nonobese subjects. We also studied associations between basal GH concentration and fasting glucose and insulin as well as between dynamic GH secretion and insulin sensitivity. Synthetic human acyl ghrelin (0.2 or 0.6 nmol/kg · h) or saline was infused in random order in 14 healthy subjects (six males, eight females; age 27.7 ± 6.3 yr; body mass index 22.0 ± 2.7 kg/m(2), mean ± SEM) on 3 separate days. Ghrelin was infused for 45 min to achieve steady-state levels and continued through a 3-h frequently sampled i.v. glucose tolerance test. Insulin sensitivity index was quantified using the minimal model of glucose kinetics. Basal 20-kDa and total GH concentrations were 0.4 ± 0.1 and 2.2 ± 0.4 ng/ml, respectively, with a 20-kDa to total GH ratio of 0.13 ± 0.02. Females had significantly higher baseline GH levels. Ghrelin administration increased 20-kDa and total GH levels in a parallel and dose-dependent fashion, with no significant change in the ratio of the isoforms. Basal 20-kDa and total GH levels were negatively correlated with fasting glucose, insulin, and homeostasis model assessment of insulin resistance. During the frequently sampled iv glucose tolerance test, GH secretion was positively correlated with insulin sensitivity index with saline infusion. Ghrelin dose-dependently increases endogenous 20-kDa and total GH secretion in a parallel fashion in healthy subjects. Both basal and stimulated levels of the different GH isoforms were positively associated with insulin sensitivity in this cohort of healthy men and women.

Effect of long term glucocorticoid treatment on human growth hormone secretion in children and adolescents and the safety and effectiveness of recombinant human growth hormone treatment.

Long term glucocorticoid (prednisolone) treatment on human growth hormone (hGH) secretion in children and adolescents and to investigate the effectiveness and safety of the recombinant human growth hormone (rhGH) treatment. Twelve patients (age: 10.4∓1.2 years) who were treated in Peking Union Medical College Hospital from September 1999 to November 2009 were enrolled in this study. All of them had taken prednisolone with a dose of 0.5∓2.0 mg/(kg.d) for 6~18 months. Two different hGH stimulating tests was done and their growth and development was evaluated at regular intervals. Seven patients were given rhGH with a dose of 0.1 U/(kg.d) for 6~12 months to improve their growth and development after half a year of prednisolone withdrawal when their disease conditions were improved. The growth speed of these 12 children decreased significantly during prednisolone treatment compared with before prednisolone treatment (1.2∓0.3cm/year vs.3.7∓1.2 cm/year,P12 months than those with a 6~12 months course (P0.05). The growth speed of seven children who received rhGH therapy for half a year were increased from 2.2∓0.1cm/year to 7.8∓0.5cm/year (P<0.05), and then to 6.9∓0.4cm/year one year later. The long-term glucocorticoid treatment can decrease the hGH secretion, and thus leads to short stature and agenesis. However, the rhGH replacement can safely and effectively improve growth and development in these children after their primary diseases are improved and glucocorticoids are withdrawn.

Growth Hormone (GH)-Releasing Hormone Increases the Expression of the Dominant-Negative GH Isoform in Cases of Isolated GH Deficiency due to GH Splice-Site Mutations

An autosomal dominant form of isolated GH deficiency (IGHD II) can result from heterozygous splice site mutations that weaken recognition of exon 3 leading to aberrant splicing of GH-1 transcripts and production of a dominant-negative 17.5-kDa GH isoform. Previous studies suggested that the extent of missplicing varies with different mutations and the level of GH expression and/or secretion. To study this, wt-hGH and/or different hGH-splice site mutants (GH-IVS+2, GH-IVS+6, GH-ISE+28) were transfected in rat pituitary cells expressing human GHRH receptor (GC-GHRHR). Upon GHRH stimulation, GC-GHRHR cells coexpressing wt-hGH and each of the mutants displayed reduced hGH secretion and intracellular GH content when compared with cells expressing only wt-hGH, confirming the dominant-negative effect of 17.5-kDa isoform on the secretion of 22-kDa GH. Furthermore, increased amount of 17.5-kDa isoform produced after GHRH stimulation in cells expressing GH-splice site mutants reduced production of endogenous rat GH, which was not observed after GHRH-induced increase in wt-hGH. In conclusion, our results support the hypothesis that after GHRH stimulation, the severity of IGHD II depends on the position of splice site mutation leading to the production of increasing amounts of 17.5-kDa protein, which reduces the storage and secretion of wt-GH in the most severely affected cases. Due to the absence of GH and IGF-I-negative feedback in IGHD II, a chronic up-regulation of GHRH would lead to an increased stimulatory drive to somatotrophs to produce more 17.5-kDa GH from the severest mutant alleles, thereby accelerating autodestruction of somatotrophs in a vicious cycle.

Drugs of abuse and the adolescent athlete

Doping with endocrine drugs is quite prevalent in amateur and professional athletes. The World Anti-Doping Agency (WADA) has a list of banned drugs for athletes who compete and a strategy to detect such drugs. Some are relatively easy, anabolic steroids and erythropoietin, and others more difficult, human growth hormone (rhGH) and insulin like growth factor I (IGF-I). The use of such compounds is likely less in adolescent athletes, but the detection that much more difficult given that the baseline secretion of the endogenous hormone is shifting during pubertal development with the greatest rise in testosterone in boys occuring about the time of peak height velocity and maximal secretion of hGH and IGF-I.This review notes the rationale, physiology, performance enhancement, adverse events and the detection of doping with insulin, rhGH, rhIGF-I, erythropoietin, and anabolic-androgenic steroids.

Expression of p25, an aberrant cyclin-dependent kinase 5 activator, stimulates basal secretion in PC12 cells.

Although alterations in the functions of neurotransmitter systems have been implicated in the pathology of Alzheimer's disease (AD), the mechanisms that give rise to these alterations are not well understood. The amount of p25, an aberrant cleavage product of p35 that activates cyclin-dependent kinase 5 (Cdk5), is elevated in AD brains. The role of Cdk5 in neurotransmitter release has been well established. In this study, we examined whether p25 was linked to altered neurotransmitter release in AD. Transient or stable expression of p25 significantly increased basal secretion of human growth hormone (hGH) or neurotransmitter in PC12 cells. Expression of a p25 phosphorylation-deficient mutant, T138A, inhibited basal hGH secretion relative to the p25 wild type, suggesting the involvement of Thr138 phosphorylation in secretion. The expression and activity of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), a key protease in the generation of beta-amyloid, are increased in AD brains. Our previous studies indicated that overexpression of BACE1 enhanced basal secretion of hGH in PC12 cells. Transient coexpression of p25 and BACE1 further stimulated spontaneous basal secretion. These results indicate a novel role for p25 in the secretory pathway and suggest that elevated levels of p25 and BACE1 in AD brains may contribute to altered neurotransmitter pathology of AD through enhancing spontaneous basal secretion.

A potential role of endogenous progesterone in modulation of GH, prolactin and thyrotrophin secretion during normal menstrual cycle

Previous studies investigating the fluctuations of endocrine secretion across the menstrual cycle yielded inconsistent results. Our objective was to evaluate during the menstrual cycle the potential role of endogenous oestradiol and progesterone in the regulation of hormones primarily controlled by the circadian clock and/or the sleep-wake cycle. Ten normally cycling young lean women were investigated once during follicular and once during luteal phase. Sleep was polygraphically recorded, and blood samples were obtained at 20-min intervals for 24 h. Sleep variables and diurnal melatonin and cortisol profiles (hormones primarily controlled by the circadian clock) were similar in both conditions. The TSH evening rise (a circadian marker) was similar in both conditions, but the sleep-related nocturnal TSH decrease occurred earlier during the luteal phase (P = 0.03) and tended to correlate positively with progesterone levels (r(s) = -0.64, P < 0.06). Daytime GH secretion and afternoon/evening PRL secretion (hormones primarily controlled by the sleep-wake homeostasis) were increased in the luteal phase compared with those of the follicular phase (GH: P = 0.04; PRL: P = 0.01). The increase in 24-h GH secretion was associated with higher progesterone levels (r(s) = 0.78, P = 0.02). In luteal phase, the evening PRL rise was associated with higher progesterone (r(s) = 0.70, P = 0.04) and oestradiol (r(s) = 0.72, P = 0.03) levels. The present data indicate that in normally cycling young women, daytime GH and PRL secretions are increased in luteal phase. These data also suggest that endogenous progesterone could play a modulation role on pituitary hormone secretion, stimulating GH and PRL release and enhancing the inhibitory action of sleep on TSH secretion.

Enhanced protein secretion from multiprotease-deficient fission yeast by modification of its vacuolar protein sorting pathway

Previously, we achieved approximately 30-fold enhanced secretion of the protease-sensitive model protein human growth hormone (hGH) by multiple gene deletion of seven obstructive proteases in the fission yeast Schizosaccharomyces pombe. However, intracellular retention of secretory hGH was found in the resultant multiprotease-deficient strains. As a solution, genetic modification of the intracellular trafficking pathway that is related to intracellular retention of hGH was attempted on a protease octuple deletant strain. Vacuolar accumulation of the intracellularly retained hGH was identified by secretory expression of hGH fused with EGFP, and three vacuolar protein sorting (vps)-deficient strains, vps10Delta, vps22Delta, and vps34Delta, were determined on account of their hGH secretion efficiency. The mutant vps10Delta was found to be effective for hGH secretion, which suggested a role for vps10 in the vacuolar accumulation of the intracellularly retained hGH. Finally, vps10 deletion was performed on the protease octuple deletant strain, which led to an approximately 2-fold increase in hGH secretion. This indicated the possible application of secretory-pathway modification and multiple protease deletion for improving heterologous protein secretion from the fission yeast S. pombe.

Cranially irradiated adult cancer survivors may have normal spontaneous GH secretion in the presence of discordant peak GH responses to stimulation tests (compensated GH deficiency)

We have previously demonstrated that spontaneous (physiological) GH secretion was entirely normal in cranially irradiated patients who had normal individual peak GH responses to the insulin tolerance test (ITT) but reduced maximal somatotroph reserve as indicated by substantially reduced group GH responses to the GHRH + arginine stimulation test (AST). The normality of spontaneous GH secretion was attributed to a compensatory increase in hypothalamic stimulatory input within a partially damaged hypothalamic-pituitary (h-p) axis. It is unknown, however, if such compensatory stimulation can also maintain normality of GH secretion in those who fail the ITT but pass the GHRH + AST. STUDY SUBJECTS AND DESIGN: We studied 24-h spontaneous GH secretion by 20-min sampling both in the fed state (n = 11) and in the last 24 h of a 33-h fast (n = 9) in adult cancer survivors with subnormal peak GH responses to the ITT but either normal or relatively less attenuated peak GH responses to the GHRH + AST. The study was conducted 8.3 +/- 1.8 (range 2-23) years after cranial irradiation for nonpituitary brain tumours (n = 9) or leukaemia/lymphoma (n = 2) in comparison with 30 normal controls (fasting, 14). Previously published diagnostic thresholds for the ITT, GHRH + AST and spontaneous GH secretion were used to characterize GH secretion. Four of the 11 patients with impaired stimulated responses to both tests showed only minor discordancies between stimulated and spontaneous GH secretion. Two of the remaining seven patients had subnormal spontaneous GH secretion. However, spontaneous GH secretion, both individually and as a group, was entirely normal in the remaining five patients who had impaired GH responses to the ITT but normal individual responses to the GHRH + AST; in these five patients, IGF-I standard deviation scores (SDS; -2.7 to -0.8) were significantly reduced to a moderate degree compared with normals. In cranially irradiated adult cancer survivors, it cannot be assumed that failure to pass the ITT in isolation reflects severe GH deficiency (GHD). It appears that in some patients near-maximal compensatory overdrive of the partially damaged somatotroph axis may result in near-normal quantitative restoration of spontaneous GH secretion, thus limiting further stimulation with the ITT to the extent that impaired GH responses can be seen even before spontaneous GH secretion starts to decline in adults. However, IGF-I status continues to provide useful information about the adequacy of the compensatory process and therefore the degree of normality of GH secretion.

Effects of Continuous Versus Intermittent Exercise, Obesity, and Gender on Growth Hormone Secretion

Obesity attenuates spontaneous GH secretion and the GH response to exercise. Obese individuals often have low fitness levels, limiting their ability to complete a typical 30-min bout of continuous exercise. An alternative regimen in obese subjects may be shorter bouts of exercise interspersed throughout the day. The objective of the study was to examine whether intermittent and continuous exercise interventions evoke similar patterns of 24-h GH secretion and whether responses are attenuated in obese subjects or affected by gender. This was a repeated-measures design in which each subject served as their own control. This study was conducted at the University of Virginia General Clinical Research Center. Subjects were healthy nonobese (n = 15) and obese (n = 14) young adults. Subjects were studied over 24 h at the General Clinical Research Center on three occasions: control, one 30-min bout of exercise, and three 10-min bouts of exercise. Twenty-four hour GH secretion was measured. Compared with unstimulated 24-h GH secretion, both intermittent and continuous exercise, at constant exercise intensity, resulted in severalfold elevation of 24-h integrated serum GH concentrations in young adults. Basal and pulsatile modes of GH secretion were attenuated both at rest and during exercise in obese subjects. The present data suggest that continuous and intermittent exercise training should be comparably effective in increasing 24-h GH secretion.