PLASMA GROWTH HORMONE RESPONSE TO INTRAVENOUS ADMINISTRATION OF AMINO ACIDS

Central and peripheral regulation of the GH/IGF-1 axis: GHRH and beyond

The regulation of growth hormone (GH) synthesis and secretion by somatotroph cells of the anterior pituitary is a highly complex process, mediated by a variety of neuroendocrine and peripheral influences. In particular, a key role is played by the hypothalamic peptides growth hormone-releasing hormone (GHRH) and somatostatin, which regulate the somatotroph axis with opposite actions, stimulating and inhibiting GH release, respectively. Since the discovery of GHRH about 50 years ago, many pathophysiological studies have explored the underlying intricate hormonal balance that regulates GHRH secretion and its interplay with the somatotroph axis. Various molecules and pathophysiological states have been shown to modulate the release of GH, GHRH, somatostatin and GH secretagogues. Collectively, the available evidence demonstrates how a vast number of neural and peripheral signals are conveyed and integrated to orchestrate a finely tuned response of the somatotroph axis that adapts to the body's varying needs for growth, metabolism, and repair. The present review aims to summarize the available evidence regarding the key regulators involved in the modulation of the somatotroph axis in humans, presenting detailed molecular insights on the signaling cascades at play. The interplay between different mechanisms governing somatotroph secretion is highlighted, underscoring the nuanced interdependence that maintains homeostasis and facilitates the body's ability to respond to internal and external stimuli.

Clinical and functional characterization of a novel KCNJ11 (c.101G > A, p.R34H) mutation associated with maturity-onset diabetes mellitus of the young type 13

PURPOSE

This study aimed to describe the clinical features, diagnostic and therapeutic course of a patient with MODY13 caused by KCNJ11 (c.101G > A, p.R34H) and how it contributes to the pathogenesis of MODY13, and to explore new therapeutic targets.

METHODS

Whole-exome sequencing was used to screen prediagnosed individuals and family members with clinically suspected KCNJ11 mutations. Real-time fluorescence quantitative PCR, western blotting, thallium flux of potassium channels, glucose-stimulated insulin secretion (GSIS), and immunofluorescence assays were used to analyze the regulation of insulin secretion by the KCNJ11 mutant in MIN6 cells. Daily blood glucose levels were continuously monitored for 14 days in the proband using the ambulatory blood glucose meter (SIBIONICS).

RESULTS

Mutation screening of the entire exon of the gene identified a heterozygous KCNJ11 (c.101G > A, p.R34H) mutation in the proband and his mother. Cell-based GSIS assays after transfection of MIN6 using wild-type and mutant plasmids revealed that this mutation impaired insulin secretory function. Furthermore, we found that this impaired secretory function is associated with reduced functional activity of the mutant KCNJ11 protein and reduced expression of the insulin secretion-associated exocytosis proteins STXBP1 and SNAP25.

CONCLUSION

For the first time, we revealed the pathogenic mechanism of KCNJ11 (c.101G > A, p.R34H) associated with MODY13. This mutant can cause alterations in KATP channel activity, reduce sensitivity to glucose stimulation, and impair pancreatic β-cell secretory function by downregulating insulin secretion-associated exocytosis proteins. Therefore, oral sulfonylurea drugs can lower blood glucose levels through pro-insulinotropic effects and are more favorable for patients with this mutation.

L-Lysine supplementation affects dietary protein quality and growth and serum amino acid concentrations in rats

Single amino acid (AA) supplementations in foods are increasing, however their potential nutritional and physiological impacts are not fully understood. This study examined the effects of L-lysine (Lys) supplementation on protein quality of diets, serum AA concentrations and associations between the ratio of supplemental Lys to dietary protein (X) with body weight gain (BWG) in Sprague-Dawley male rats. Rats were fed one of 10 diets containing either 7% or 20% casein and supplemented with 0% (Control), 1.5%, 3%, 6% Lys or 6% Lys + 3% L-arginine (Arg) (8 rats/diet group) for 1 week. Lys supplementation reduced the protein quality of the casein-based diets (p < 0.01). BWG was reduced by supplemental Lys when X > 0.18. Free Lys supplementation dose-dependently increased serum Lys levels (p < 0.01), while increased protein-bound Lys (1.4% vs 0.52%) had little effect on serum Lys (p > 0.05). In the 7% casein diets, ≥ 1.5% supplemental Lys reduced serum alanine, asparagine, glycine, isoleucine, leucine, serine, tyrosine, valine, carnitine, ornithine, and increased urea. Supplementation of ≥ 3% Lys additionally reduced tryptophan and increased histidine, methionine and α-aminoadipic acid (α-AAA) compared to the Control (p < 0.05). In the 20% casein diets, addition of ≥ 1.5% Lys reduced serum asparagine and threonine, and ≥ 3% Lys reduced leucine, proline, tryptophan, valine, and ornithine, and 6% Lys reduced carnitine, and increased histidine, methionine, and α-AAA. Overall, this study showed that free Lys supplementation in a Lys-sufficient diet reduced the protein quality of the diets and modified the serum concentrations of many amino acids. Excess free Lys intake adversely affected growth and utilization of nutrients due to AA imbalance or antagonism. Overall lower protein intake increases susceptibility to the adverse effects of Lys supplementation.

Mechanisms of ageing: growth hormone, dietary restriction, and metformin

Tackling the mechanisms underlying ageing is desirable to help to extend the duration and improve the quality of life. Life extension has been achieved in animal models by suppressing the growth hormone-insulin-like growth factor 1 (IGF-1) axis and also via dietary restriction. Metformin has become the focus of increased interest as a possible anti-ageing drug. There is some overlap in the postulated mechanisms of how these three approaches could produce anti-ageing effects, with convergence on common downstream pathways. In this Review, we draw on evidence from both animal models and human studies to assess the effects of suppression of the growth hormone-IGF-1 axis, dietary restriction, and metformin on ageing.

Impact of dietary supplementation of l-Arginine, l-Glutamine, and the combination of both on nursing performance of multiparous sows

Dietary supplementation with arginine (Arg) or glutamine (Gln) has been considered as an option to improve nursing performance in reproductive sows. This study investigated whether a low-level supplementation of Arg or Gln or a blend of both could modify milk nutrients and improve piglets' growth beyond weaning. Seventy-two multiparous sows were assigned to four groups: one group fed a control diet, three treatment groups fed the control diet supplemented with either 0.35% Arg, 0.35% Gln, or both, from day 108 of gestation until weaning at day 26 of lactation. Immediately after birth, the litters were cross fostered to 13 piglets and monitored until 2 wk after weaning. Sows body condition and litter growth were assessed. Colostrum and milk samples were collected for nutrient analyses. Plasma concentrations of insulin-like growth factor 1 (IGF-1) around weaning were determined in sows and two representative piglets per litter. Supplementing Gln or the combination of Arg and Gln had no effect on the parameters studied. Arg supplementation increased weaning weight, while decreasing the variation of piglet weights 2 wk after weaning. There was no correlation with plasma IGF-1 since the hormone was not altered in sows or piglets. The colostral concentration of fat tended to increase in the Arg-group, whereas protein, lactose, energy, and polyamine concentrations remained unaffected. Milk samples obtained on day 12 and 25 of lactation were not influenced by dietary treatment. The data indicate that there might be a window of opportunity, explicitly at the onset of lactation, for dietary intervention by maternal dietary Arg supplementation.

Growth Hormone Response to L-Arginine Alone and Combined with Different Doses of Growth Hormone-Releasing Hormone: A Systematic Review and Meta-Analysis

Background

Arginine (ARG) can modulate growth hormone (GH) release by suppressing its endogenous inhibitory regulator, somatostatin. ARG also induces the release of the GH-releasing hormone (GHRH). This study aims to review the effects of L-arginine supplementation alone and combined with GHRH in different doses on GH secretion.

Methods

In this systematic review and meta-analysis, an electronic literature search was conducted on Medline database (PubMed), Scopus, and Web of Science databases. All eligible studies were randomized clinical trials that reported the effects of ARG supplementation alone or with GHRH on GH levels. Mean difference (MD) and 95% confidence intervals (CI) were computed as the effect size.

Results

Meta-analyses showed significant effects of ARG alone on GH release (MD = 10.07, 95% CI: 7.87, 12.28). Moreover, the response of GH was greater with ARG in combination with GHRH (MD = 24.96, 95% CI: 17.51, 32.42). There was no significant difference between the patients and healthy individuals and between oral and injection use of ARG. The systematic review revealed the important role of ARG in combination with other amino acids on GH secretion in patients with GH deficiency.

Conclusion

This study revealed that in GH-deficient individuals, high doses of ARG supplementation in combination with GHRH and/or other amino acids might have potential therapeutic effects on increasing GH concentrations. These findings propose that ARG supplementation can be considered as a potential stimulator in management of GH deficiency.

Regulation of GH and GH Signaling by Nutrients

Growth hormone (GH) and insulin-like growth factor-1 (IGF-I) are pleiotropic hormones with important roles in lifespan. They promote growth, anabolic actions, and body maintenance, and in conditions of energy deprivation, favor catabolic feedback mechanisms switching from carbohydrate oxidation to lipolysis, with the aim to preserve protein storages and survival. IGF-I/insulin signaling was also the first one identified in the regulation of lifespan in relation to the nutrient-sensing. Indeed, nutrients are crucial modifiers of the GH/IGF-I axis, and these hormones also regulate the complex orchestration of utilization of nutrients in cell and tissues. The aim of this review is to summarize current knowledge on the reciprocal feedback among the GH/IGF-I axis, macro and micronutrients, and dietary regimens, including caloric restriction. Expanding the depth of information on this topic could open perspectives in nutrition management, prevention, and treatment of GH/IGF-I deficiency or excess during life.

The GH Axis in Relation to Accepting an Early Macronutrient Deficit and Outcome of Critically Ill Patients

CONTEXT

Changes in the GH axis during critical illness resemble fasting in healthy adults and contribute to hypercatabolism, which potentially affects outcome. Accepting macronutrient deficits by withholding parenteral nutrition (PN) during the first week in the intensive care unit (ICU; late PN) reduced complications and accelerated recovery as compared with early use of PN (early PN).

OBJECTIVE

To investigate how late PN affects the GH axis in relation to its clinical outcome benefits.

DESIGN

Preplanned subanalysis of the Early Parenteral Nutrition Completing Enteral Nutrition in Adult Critically Ill Patients randomized controlled trial.

PARTICIPANTS

A total of 1128 patients for time-course study, 20 patients investigated for nocturnal GH pulsatility, and 600 patients investigated for muscle weakness, with early PN and late PN patients having comparable baseline characteristics.

INTERVENTION

Withholding PN during the first ICU week (late PN) vs early PN.

MAIN OUTCOME MEASURES

Changes in serum GH, IGF-I, IGF-binding protein (IGFBP) 3, and IGFBP1 concentrations from ICU admission to day 4 or last ICU day for patients with a shorter ICU stay (d4/LD) and association in multivariable analyses with likelihood of earlier live ICU discharge, risk of new infection, and muscle weakness.

RESULTS

Late PN attenuated a rise in serum GH and IGF-I (P < 0.0001), did not affect IGFBP3, and attenuated a decrease in IGFBP1 concentrations from admission to d4/LD (P < 0.0001) as compared with early PN. Late PN decreased nonpulsatile (P = 0.005), but not pulsatile, GH secretion. Adjusting the multivariable models for the observed GH axis alterations increased the independent benefit of late PN for all outcomes. GH axis alterations induced by late PN were independently associated with adverse outcomes (P ≤ 0.03).

CONCLUSION

Accepting macronutrient deficits early during critical illness further suppressed the GH axis, which statistically attenuated its clinical outcome benefits.

Do anabolic nutritional supplements stimulate human growth hormone secretion in elderly women with heart failure?

Growth hormone treatment has gained attention over the past decade as a treatment for heart failure. Human growth hormone (HGH) must be administered by injections (usually daily), so there is considerable advantage to stimulation of endogenous secretion by amino acid-based nutritional supplementation. However, studies investigating the effect of amino acid (AA) supplementation show conflicting results. Therefore, in this study we aimed to investigate the effect of nutritional supplementation on HGH production in elderly women with heart failure. Eight elderly women with heart failure participated in this randomized cross-over study. Plasma HGH concentration was measured before and for 4 h following ingestion of a mixture of protein, carbohydrate, and fat or an AA beverage. HGH concentration was determined with ELISA kits and AA concentrations were analyzed by Liquid Chromatography-Mass Spectrometry (LCMS). Linear mixed models was performed to analyze the effect of time, treatment, and interaction. Plasma arginine and lysine concentrations were significantly higher after consumption of the AA drink compared to the mixture of protein, carbohydrate, and fat. Nonetheless, only ingestion of the protein, carbohydrate, and fat mixture (meal replacement) increased HGH concentration. HGH concentration was increased in elderly women with heart failure following consumption of a meal replacement containing protein, carbohydrate, and fat. Consumption of a mixture of amino acids failed to increase HGH concentration despite significantly greater elevations in plasma amino acid concentrations, including arginine and lysine. The stimulatory effect of the protein/carbohydrate/fat mixture was presumably mediated by factors other than increases in free amino acid concentrations.

Dietary Intake of Protein in Early Childhood Is Associated with Growth Trajectories between 1 and 9 Years of Age

BACKGROUND

High protein intake in infancy might lead to a higher body mass index (BMI) in childhood. However, whether these associations differ between different sources of protein is unclear.

OBJECTIVE

We investigated associations between the intake of total protein, protein from different sources, and individual amino acids in early childhood and repeatedly measured height, weight, and BMI up to the age of 9 y.

METHODS

This study was performed in 3564 children participating in the Generation R Study, a population-based prospective cohort study in Rotterdam, Netherlands. Intakes of total protein, animal protein, vegetable protein, and individual amino acids (including methionine, arginine, lysine, threonine, valine, leucine, isoleucine, phenylalanine, tryptophan, histidine, cysteine, tyrosine, alanine, asparagine, glutamine, glycine, proline, and serine) at 1 y were assessed by using a food-frequency questionnaire. Height and weight were measured at the approximate ages of 14, 18, 24, 30, 36, and 45 mo and at 6 and 9 y, and BMI was calculated.

RESULTS

After adjustment for confounders, linear mixed models showed that a 10-g higher total protein intake/d at 1 y was significantly associated with a 0.03-SD greater height (95% CI: 0.00, 0.06), a 0.06-SD higher weight (95% CI: 0.03, 0.09), and a 0.05-SD higher BMI (95% CI: 0.03, 0.08) up to the age of 9 y. Associations were stronger for animal than for vegetable protein intake but did not differ between dairy and nondairy animal protein or between specific amino acids.

CONCLUSIONS

A higher intake of protein, especially animal protein, at 1 y of age was associated with a greater height, weight, and BMI in childhood up to 9 y of age. Future studies should explore the role of growth hormones and investigate whether protein intake in early childhood affects health later in life.

Tissue-specific regulation of potassium homeostasis by high doses of cationic amino acids

The administration of l-arginine hydrochloride has been used for testing pituitary secretion in humans, and as an experimental model for induction of acute pancreatitis in rats and mice. Whereas in the first case, the administration of the amino acid is associated with hiperkalemia, in the model of acute pancreatitis no data are available on possible changes in potassium homeostasis. The present study shows that the acute administration to mice of l-arginine hydrochloride or other cationic amino acids almost duplicate plasma potassium levels. This effect was associated to a marked decrease of tissue potassium in both pancreas and liver. No changes were found in other tissues. These changes cannot be ascribed to the large load of chloride ions, since similar effects were produced when l-ornithine aspartate was administered. The changes in potassium levels were dependent on the dose. The displacement of intracellular potassium from the liver and pancreas to the extracellular compartment appears to be dependent on the entry of the cationic amino acid, since the administration of an equivalent dose of alfa-difluoromethyl ornithine HCl (DFMO), a non physiological analog of l-ornithine, which is poorly taken by the tissues in comparison with the physiological cationic amino acids, did not produce any change in potassium levels in pancreas and liver. The analyses of the expression of cationic amino acid transporters (CAT) suggest that the CAT-2 transporter may be implicated in the potassium/cationic amino acid interchange in liver and pancreas. The possible physiological or pathological relevance of these findings is discussed.

Growth Hormone Deficiency and Lysinuric Protein Intolerance: Case Report and Review of the Literature

BACKGROUND

Lysinuric protein intolerance (LPI; MIM# 222700) is a rare metabolic disorder caused by a defective cationic amino acids (CAA) membrane transport leading to decreased circulating plasma CAA levels and resulting in dysfunction of the urea cycle. Short stature is commonly observed in children with LPI and has been associated with protein malnutrition. A correlation between LPI and growth hormone deficiency (GHD) has also been postulated because of the known interaction between the AA arginine, ornithine, and lysine and growth hormone (GH) secretion. Our report describes a case of GHD in an LPI patient, who has not presented a significant increase in growth velocity with recombinant-human GH (rhGH) therapy, suggesting some possible pathogenic mechanisms of growth failure.

CASE PRESENTATION

The proband was a 6-year-old boy, diagnosed as suffering from LPI, erythrophagocytosis (HP) in bone marrow, and short stature. Two GH provocative tests revealed GHD. The patient started rhGH therapy and a controlled-protein diet initially with supplementation of oral arginine and then of citrulline. At 3-year follow-up, no significant increase in growth velocity and in insulin-like growth factor-1 (IGF-1) levels was observed. Inadequate nutrition and low plasmatic levels of arginine, ornithine, lysine, and HP may have contributed to his poor growth.

CONCLUSION

Our case suggests that growth failure in patients with GHD and LPI treated with rhGH could have a complex and multifactorial pathogenesis. Persistently low plasmatic levels of lysine, arginine, and ornithine, associated with dietary protein and caloric restriction and systemic inflammation, could determine a defect in coupling GH to IGF-1 production explaining why GH replacement therapy is not able to significantly improve growth impairment. We hypothesize that a better understanding of growth failure pathophysiology in these patients could lead to the development of more rational strategies to treat short stature in patients with LPI.

Analysis of Selected Amino Acids in Different Varieties of Wheat Available in Punjab, Pakistan

A validated method is proposed to check amino acids variability among eighty-nine wheat samples collected from Punjab province of Pakistan during 2012-2013. Orthophthalaldehyde along with 2-mercaptoethanol was used as a derivatizing reagent that showed florescence at detection wavelength of Ex of 340 nm and Em of 450 nm under suitable pH range of 9-10. RP-HPLC-FLD system employed was Agilent 1100 series equipped with Eclipse XDB C-18 column (2.1 × 150 mm, 5 µ) and column temperature was maintained at 40°C. The maximum concentration of aspartic acid, glutamic acid, leucine, arginine, and histidine was found in Vehari (0.496 g/100 g), Rajanpur (1.292 g/100 g), Rahim Yar khan (0.60 g/100 g), Bahawalpur (0.662 g/100 g), and Narowal (0.377 g/100 g), respectively, while the minimum in Narowal (0.13 g/100 g), Vehari (0.706 g/100 g), Narowal (0.339 g/100 g), Muzaffargarh (0.14 g/100 g), and Rahim Yar Khan (0.088 g/100 g) among the samples obtained from districts. Wheat variety Pb-11 contained relatively high aspartic acid (0.297 g/100 g), glutamic acid (0.897 g/100 g), and leucine (0.484 g/100 g) whereas variety Ass-11 had arginine (0.895 g/100 g) and histidine (0.266 g/100 g). The amino acids were found to vary as follows: aspartic acid 0.130–0.496, glutamic acid 0.706–1.292, leucine 0.321–0.6, arginine 0.118–0.895, and histidine 0.088–0.377 g/100 g flour. The accuracy was in the range of 95.88–100.67%, whereas the RSD for precision was not more than 1.40 for all amino acids.

Regulation of skeletal muscle protein degradation and synthesis by oral administration of lysine in rats

Several catabolic diseases and unloading induce muscle mass wasting, which causes severe pathological progression in various diseases and aging. Leucine is known to attenuate muscle loss via stimulation of protein synthesis and suppression of protein degradation in skeletal muscle. The aim of this study was to investigate the effects of lysine intake on protein degradation and synthesis in skeletal muscle. Fasted rats were administered 22.8-570 mg Lys/100 g body weight and the rates of myofibrillar protein degradation were assessed for 0-6 h after Lys administration. The rates of myofibrillar protein degradation evaluated by MeHis release from the isolated muscles were markedly suppressed after administration of 114 mg Lys/100 g body weight and of 570 mg Lys/100 g body weight. LC3-II, a marker of the autophagic-lysosomal pathway, tended to decrease (p=0.05, 0.08) after Lys intake (114 mg/100 g body weight). However, expression of ubiquitin ligase E3 atrogin-1 mRNA and levels of ubiquitinated proteins were not suppressed by Lys intake. Phosphorylation levels of mTOR, S6K1 and 4E-BP1 in the gastrocnemius muscle were not altered after Lys intake. These results suggest that Lys is able to suppress myofibrillar protein degradation at least partially through the autophagic-lysosomal pathway, not the ubiquitin-proteasomal pathway, whereas Lys might be unable to stimulate protein synthesis within this time frame.

Muscle protein metabolism during compensatory growth with changing dietary lysine levels from deficient to sufficient in growing rats

Livestock and laboratory animals show compensatory growth when they are fed ad libitum following a period of restriction feeding. Lysine is a major limiting essential amino acid in the diets both for humans and animals. We hypothesized that changing dietary lysine levels from deficient to sufficient induced compensatory growth in young rats. We elucidated the effect of lysine sufficiency on the dynamics of hormones, relevant to muscle protein synthesis and degradation, insulin-like growth factor-I (IGF-I) and corticosterone, and on the expression of proteolytic-related genes in skeletal muscle during compensatory growth. Lysine sufficiency where the dietary lysine level was increased from 0.46% to 1.30% after 2 wk of subjecting the rats to the lower lysine level induced 80% enhancement of growth rate of rats. During compensatory growth with the lysine sufficiency, fractional muscle protein synthesis rates were higher whereas fractional muscle protein degradation rates were lower than those of the control group (p<0.05). After lysine sufficiency, the expression of atrogin-1/MAFbx mRNA was decreased in gastrocnemius muscle (p<0.05). With the lysine sufficiency, serum IGF-I concentration increased (p<0.05) whereas serum corticosterone decreased (p<0.05). These findings suggest that compensatory growth with lysine sufficiency is due to a change of hormone levels before and after changing diets, resulting in incrementation of protein synthesis and suppression of protein degradation of skeletal muscle.

Effect of a high-protein diet on ghrelin, growth hormone, and insulin-like growth factor-I and binding proteins 1 and 3 in subjects with type 2 diabetes mellitus

We have developed a diet that over 5 weeks dramatically lowers plasma glucose in people with type 2 diabetes mellitus. This diet consists of 30% carbohydrate, 30% protein, and 40% fat and is referred to as a Low Biologically Available Glucose (LoBAG) diet. The diet also resulted in an approximately 30% increase in fasting insulin-like growth factor-I (IGF-I). Thus, we were interested in determining if the IGF-I elevation was due to an increase in ghrelin and growth hormone (GH) or to a change in IGF-I binding proteins (IGFBPs). Eight men with type 2 diabetes mellitus ingested a control diet (15% protein, 55% carbohydrate, and 30% fat) and a LoBAG(30) diet for 5 weeks in a randomized crossover design with a washout period in between. Before and after each 5-week period, subjects had blood drawn for total glycated hemoglobin and, at several time points over 24 hours, for GH, IGF-I, IGFBP-1, IGFBP-3, ghrelin, glucose, and insulin. Fasting and 24-hour glucose concentrations and total glycated hemoglobin were decreased, as expected (all Ps < .05). Fasting IGF-I increased by approximately 30% (P = .05) and remained unchanged throughout 24 hours. Ghrelin, GH, IGFBP-1, IGFBP-3, and insulin were not different between diets. Insulin and IGFBP-1 concentrations were reciprocal, as expected. Insulin-like growth factor-I binding protein 1 decreased as insulin increased to greater than approximately 30 to 40 μU/mL. Ingestion of a LoBAG(30) diet by weight-stable subjects with type 2 diabetes mellitus resulted in an increase in total IGF-I without an increase in ghrelin, GH, and IGFBP-3 or a change in IGFBP-1 regulation. The mechanism remains to be determined.

The effects of dietary protein on the somatotropic axis: a comparison of soy, gelatin, alpha-lactalbumin and milk

BACKGROUND/OBJECTIVES

Growth hormone (GH) is an important regulator of growth and body composition. It has been shown that GH release can be promoted by administration of various amino acids (AAs), such as arginine and lysine, that are present in soy protein. We previously showed that oral ingestion of soy protein stimulates the GH release, it is not known however to which extent other proteins stimulate the GH secretion.

SUBJECTS/METHODS

Ingestion of soy protein (soy), gelatin protein (gelatin), alpha-lactalbumin protein (alpha-lactalbumin) and milk protein (milk) were compared on their GH-stimulating capacity. After oral ingestion of protein (0.6 g protein per kg bodyweight), blood was sampled every 20 min for 5 h to analyze GH, AA, insulin and glucose concentrations. The study was performed in eight healthy women (aged 19-26 years; body mass index 19-26 kg/m(2)) in a randomized, single blind, placebo-controlled crossover design.

RESULTS

GH responses were more increased after ingestion of gelatine (8.2+/-1.1 microg/l) compared with ingestion of soy, alpha-lactalbumin and milk (5.0+/-0.8, 4.5+/-0.6 and 6.4+/-1.0 microg/l, respectively) (P<0.05). After ingestion of each protein, GH responses were higher compared with placebo ingestion (P<0.05). Simultaneously ingestion of gelatin resulted in the highest serum-arginine concentrations (ARG) compared with after ingestion of the other proteins (P<0.05). Insulin as well as glucose concentrations were not different after ingestion of the various proteins (P<0.05).

CONCLUSIONS

The GH-promoting activity of protein depends on the protein source, in that, gelatin protein is the most potent GH stimulator. Arginine may be the responsible AA in the GH-promoting effect of gelatin, although each protein may have its own specific AA-spectrum involved in the stimulation of the somatotropic axis.

Association between intake of dietary protein and 3-year-change in body growth among normal and overweight 6-year-old boys and girls (CoSCIS)

OBJECTIVE

Growth hormone (GH) affects linear growth and body composition, by increasing the secretion of insulin-like growth factor-I (IGF-I), muscle protein synthesis and lipolysis. The intake of protein (PROT) as well as the specific amino acids arginine (ARG) and lysine (LYS) stimulates GH/IGF-I secretion. The present paper aimed to investigate associations between PROT intake as well as intake of the specific amino acids ARG and LYS, and subsequent 3-year-change in linear growth and body composition among 6-year-old children.

DESIGN

Children's data were collected from Copenhagen (Denmark), during 2001-2002, and again 3 years later. Boys and girls were separated into normal weight and overweight, based on BMI quintiles. Fat-free mass index (FFMI) and fat mass index (FMI) were calculated. Associations between change (Delta) in height, FMI and FFMI, respectively, and habitual PROT intake as well as ARG and LYS were analysed by multiple linear regressions, adjusted for baseline height, FMI or FFMI and energy intake, age, physical activity and socio-economic status.

SETTING

Eighteen schools in two suburban communities in the Copenhagen (Denmark) area participated in the study.

SUBJECTS

In all, 223 children's data were collected for the present study.

RESULTS

High ARG intake was associated with linear growth (beta = 1.09 (se 0.54), P = 0.05) among girls. Furthermore, in girls, DeltaFMI had a stronger inverse association with high ARG intake, if it was combined with high LYS intake, instead of low LYS intake (P = 0.03). No associations were found in boys.ConclusionIn prepubertal girls, linear growth may be influenced by habitual ARG intake and body fat gain may be relatively prevented over time by the intake of the amino acids ARG and LYS.

Somatotropic responses to soy protein alone and as part of a meal

CONTEXT

GH is an important regulator of growth and body composition. We previously showed that GH release can be promoted by oral ingestion of soy protein; it is not known, however, whether these somatotropic effects of soy protein are also present when soy protein is ingested as part of a complete meal.

OBJECTIVE/DESIGN

We compared the effects of oral ingestion of soy protein alone with the effects of a meal containing the same amount of soy protein on GH secretion in six healthy women (body mass index 19-26 kg/m(2), 19-36 years), in a randomized crossover design. During the whole experiment, serum GH, insulin, and glucose were determined every 20 min.

RESULTS

GH responses as determined by area under the curve (AUC) and peak values were lower after ingestion of the meal, in comparison with GH responses after the soy protein consumption alone (P<0.05), and did not differ from the placebo. Glucose and insulin responses, both determined as AUC and peak values, were higher after ingestion of the meal, compared with those after ingestion of the protein drink or the placebo (P<0.05).

CONCLUSION

The somatotropic effect of soy protein is reduced and delayed when soy protein is ingested as part of a complete meal. Dietary carbohydrates, by increasing serum levels of glucose and insulin concentration, as well as dietary fat, may have interfered with the somatotropic effects of soy protein.

Normal physiology of hypothalamic pituitary regulation

The anterior pituitary is a complex heterogeneous gland that exerts a central role in the integration of several regulatory systems. Its six key hormones affect peripheral glands or target tissues and are essential for reproduction, growth and development, metabolism, adaptation to external environmental changes, and stress. Each of the pituitary hormones is regulated by the central nervous system through neuroendocrine pathways involving the hypothalamus, by feedback effects from peripheral target gland hormones, and by intrapituitary mechanisms. The hormones are secreted in a pulsatile manner, which is distinct for each hormone and reflects the influence of its individual neuroendocrine control mechanisms.

Effects of oral ingestion of amino acids and proteins on the somatotropic axis

CONTEXT

GH is an important regulator of growth and body composition. It has been shown that GH release can be promoted by iv as well as oral administration of various amino acids (AAs), especially arginine (ARG) and lysine (LYS), which are amply present in soy protein. However, the effects of dietary protein on GH secretion are less well described.

OBJECTIVE AND DESIGN

In an experiment, we compared the effects of oral ingestion of a mixture reflecting the AA composition of soy protein (AA), with oral ingestion of ARG + LYS, on GH secretion in eight healthy women (body mass index 19-25 kg/m(2); age, 18-24 yr). In a second experiment, we compared oral ingestion of hydrolyzed soy protein and complete soy protein with the AA mixture on GH secretion in eight healthy women (body mass index 19-26 kg/m(2); age, 19-36 yr). Both experiments were performed in a randomized, single-blind crossover design. GH, insulin, glucose, and plasma AA were determined every 20 min, during 3 h in the first experiment and during 5 h in the second experiment.

RESULTS

Peak values of GH were higher after ingestion of the AA mixture compared with ingestion of ARG + LYS (P < 0.05). GH responses, as determined by area under the curve, did not significantly differ after ingestion of the complete soy protein, hydrolyzed soy protein, or AA mixture but were all higher than after placebo (P < 0.05). Insulin responses (area under the curve) were higher after ingestion of hydrolyzed soy protein, complete soy protein, and AA mixture, compared with placebo (P < 0.05). Glucose concentrations were unaffected.

CONCLUSION

Ingestion of soy protein, either hydrolyzed or intact, as well as AAs reflecting soy protein, stimulates GH release to a similar extent.

Growth hormone, arginine and exercise

PURPOSE OF REVIEW

To describe the effect of an acute bout of exercise on growth hormone responses and to discuss the effect of L-arginine supplementation on growth hormone responses.

RECENT FINDINGS

Recent studies have shown that resting growth hormone responses increase with oral ingestion of L-arginine and the dose range is 5-9 g of arginine. Within this range there is a dose-dependent increase and higher doses are not well tolerated. Most studies using oral arginine have shown that arginine alone increases the resting growth hormone levels at least 100%, while exercise can increase growth hormone levels by 300-500%. The combination of oral arginine plus exercise attenuates the growth hormone response, however, and only increases growth hormone levels by around 200% compared to resting levels.

SUMMARY

Exercise is a very potent stimulator of growth hormone release and there is considerable research documenting the dramatic growth hormone rise. At rest oral L-arginine ingestion will enhance the growth hormone response and the combination of arginine plus exercise increases growth hormone, but this increase may be less than seen with exercise alone. This diminished response is seen in both in both younger and older individuals.

Efeito da suplementação de L-arginina sobre a secreção de hormônio do crescimento e fator de crescimento semelhante à insulina em adultos

Baseado nos pressupostos de que a infusão de aminoácidos pode aumentar a secreção de hormônio de crescimento (GH), e que o metabolismo deste hormônio está relacionado com a secreção do fator de crescimento semelhante à insulina (IGF-I), o objetivo deste estudo foi verificar o efeito da suplementação de L-arginina sobre o GH e IGF-I em adultos. Participaram do estudo 17 indivíduos do sexo masculino, que foram randomizados para receber L-arginina (n= 10) ou placebo (n= 7), sete gramas ao dia, durante um período de sete dias. Antes e após o período de suplementação, os voluntários realizaram coleta de sangue em jejum para verificação dos níveis séricos de GH e IGF-I, bem como coleta de urina para verificação da excreção de uréia. Ao final do período experimental, verificamos que o grupo que recebeu L-arginina aumentou a excreção de uréia na urina (de 2684,1 ± 475,2 mg/dl para 2967,2 ± 409,7 mg/dl, p= 0,002), entretanto não modificou significativamente a secreção dos hormônios avaliados. O grupo que recebeu placebo não alterou significativamente nenhum parâmetro avaliado. A suplementação de L-arginina durante sete dias mostrou-se ineficaz para aumentar a secreção de GH e IGF-I em indivíduos adultos do sexo masculino.

Growth hormone deficiency in a patient with lysinuric protein intolerance

INTRODUCTION

Lysinuric protein intolerance (LPI; MIM 222700) is a rare, autosomal recessive metabolic disorder caused by mutations in the SLC7A7 gene, which encodes the light chain of the cationic amino acids (CAA) transporter y+. The clinical presentation of LPI includes gastrointestinal symptoms, failure to thrive, episodes of coma, hepatosplenomegaly and osteoporosis. However, other findings have also been reported, and these suggest a multisystem involvement.

DISCUSSION

We report a girl with confirmed LPI who presented with severe short stature that was unresponsive to adequate LPI treatment. The girl was found to have a classic growth hormone deficiency (GHD) and responded well to growth hormone (GH) replacement therapy.

CONCLUSION

While it is not known whether the mechanisms involved in the GHD of our patient are related to LPI, this case suggests that GH/IGF-I axis should be investigated in LPI children with persistent growth failure.

Arginine supplementation and wound healing

Modern advances in nutritional therapies have led to the specific use of arginine supplementation for protein synthesis, cell signaling through the production of nitric oxide, and cell proliferation through its metabolism to ornithine and to polyamines. Arginine is classified as a nonessential amino acid that becomes a conditionally essential substrate in stressed adults. Arginine has been shown to enhance wound strength and collagen deposition in artificial incisional wounds in rodents and humans. A role for dietary intervention in the form of arginine supplementation has been proposed to normalize or enhance wound healing in humans. Although this hypothesis is frequently discussed, the therapeutic effect of arginine supplementation on chronic wound healing in humans is still undetermined and requires further objective evidence. Well-designed clinical trials are required to determine whether arginine supplementation is effective in enhancing healing of acute and chronic wounds in humans and how much arginine is recommended to meet metabolic needs during the phases of wound healing.

Arginine and immunity: a unique perspective

Arginine functions in the body as a free amino acid, a component of most proteins, and the substrate for several non-protein, nitrogen-containing compounds, many of which function in immunity. Although arginine is synthesized in the body, it is not made in sufficient quantities to support growth or meet metabolic requirements during periods of stress. Based on the biochemical and physiological role of arginine in maintaining health and immunity, arginine is being added at pharmacologic concentrations to enteral formulas to boost immune function. Unfortunately, animal and human studies that investigate enteral arginine supplementation as the single variable do not show clear immunologic benefit. The inconsistent effects of arginine supplementation on immune function are due to numerous factors, such as the amount and timing of arginine supplementation, the animal species or strain of species, and the experimental model. Systematic study is required to determine whether a basal dietary intake of arginine is required to maintain immune function during health and how much arginine is required to meet metabolic requirements during periods of growth or stress.

Use of amino acids as growth hormone-releasing agents by athletes

Specific amino acids, such as arginine, lysine and ornithine, can stimulate growth hormone (GH) release when infused intravenously or administered orally. Many individuals consume amino acids before strength training workouts, believing this practice accentuates the exercise-induced GH release, thereby promoting greater gains in muscle mass and strength. The GH response to amino acid administration has a high degree of interindividual variability and may be altered by training status, sex, age, and diet. Although parenteral administration consistently leads to increased circulating GH concentration, oral doses that are great enough to induce significant GH release are likely to cause stomach discomfort and diarrhea. During exercise, intensity is a major determinant of GH release. Although one study showed that arginine infusion can heighten the GH response to exercise, no studies found that pre-exercise oral amino acid supplementation augments GH release. Further, no appropriately conducted scientific studies found that oral supplementation with amino acids, which are capable of inducing GH release, before strength training increases muscle mass and strength to a greater extent than strength training alone. The use of specific amino acids to stimulate GH release by athletes is not recommended.

GH/IGF-I axis in anorexia nervosa

Patients with anorexia nervosa (AN) may develop multiple endocrine abnormalities, including amenorrhea, hyperactivity of the hypothalamus-pituitary-adrenal axis, hypothyroidism and particular changes in the activity of the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis. Exaggerated GH secretion and reduced IGF-I levels are usually found in AN, as well as in conditions of malnutrition and malabsorption, insulin-dependent diabetes mellitus, liver cirrhosis and catabolic states. In AN, GH hypersecretion at least partially reflects malnutrition-induced peripheral GH resistance, which leads to reduced IGF-I synthesis and release; this implies an impairment of the negative IGF-I feedback action on GH secretion. On the other hand, primary alterations in the neural control of GH secretion cannot be ruled out. The neuroendocrine alterations include enhanced somatotroph responsiveness to growth hormone releasing hormone (GHRH) and impaired GH response to most central nervous system-mediated stimuli. Particular resistance to cholinergic manipulation has also been demonstrated, thus suggesting a somewhat specific alteration in the somatostatin (SS)-mediated cholinergic influence on GH secretion. Moreover, paradoxical GH responses to glucose load, thyrotropin releasing hormone (TRH) and luteinizing hormone releasing hormone (LHRH) have also been reported. The effect of reduced leptin levels on GH hypersecretion in AN is still unclear, but ghrelin (the gastric hormone that is a natural ligand of the GH secretagogue receptor and strongly stimulates somatotroph secretion) is thought to play a major role. Regardless of the supposed central and peripheral alterations, it has to be emphasised that the activity of the GH/IGF-I axis in AN is generally restored by nutritional and stable weight gain. It therefore reflects an impaired nutritional state and cannot be considered a primary hallmark of the disease.

Administration and (1)H MRS detection of histidine in human brain: application to in vivo pH measurement

Measurement of histidine in vivo offers the potential for tissue pH measurement using routinely performed (1)H MR spectroscopy. In the brain, however, histidine concentrations are generally too low for reliable measurement. By using oral loading of histidine, this study demonstrates that brain concentrations can be significantly increased, enabling detection of histidine by localized (1)H MR measurements and making in vivo pH measurement possible. In studies carried out on healthy human subjects at 1.5 T, a consistent spectral quality downfield from water was achieved using a PRESS sequence at short echo times. Measurements at different TE values helped to characterize the downfield spectral region. Histidine loading of 400 mg/kg of body weight increased brain histidine levels by approximately 0.8 mM, with maximum histidine concentration reached 4 to 7 hr after consumption. The pH calculated from histidine resonances was 6.96, and a hyperventilation study demonstrated the potential for measuring altered pH.

Amino acid supplements to improve athletic performance

This review provides a critical evaluation of the metabolic rationale for the use of individual amino acids as nutritional ergogenic (work-generating) aids in athletes. The conclusion is that in contrast to the claims made on sport nutrition products, branched-chain amino acids do not improve endurance performance, that the evidence that glutamine supplements may improve immune function is rather weak, and that the available commercial supplements contain too little arginine to increase growth hormone levels. No studies have been performed to investigate the claim that tyrosine supplements can improve explosive exercise.

Cloning and functional expression of a human Na(+) and Cl(-)-dependent neutral and cationic amino acid transporter B(0+)

A Na(+)-dependent neutral and cationic amino acid transport system (B(0+)) plays an important role in many cells and tissues; however, the molecular basis for this transport system is still unknown. To identify new transporters, the expressed sequence tag database was queried, and cDNA fragments with sequence similarity to the Na(+)/Cl(-)-dependent neurotransmitter transporter family were identified. Based on these sequences, rapid amplification of cDNA ends of human mammary gland cDNA was used to obtain a cDNA of 4.5 kilobases (kb). The open reading frame encodes a 642-amino acid protein named amino acid transporter B(0+). Human ATB(0+) (hATB(0+)) is a novel member of the Na(+)/Cl(-)-dependent neurotransmitter transporter family with the highest sequence similarity to the glycine and proline transporters. Northern blot analysis identified transcripts of approximately 4.5 kb and approximately 2 kb in the lung. Another tissue survey suggests expression in the trachea, salivary gland, mammary gland, stomach, and pituitary gland. Electrophysiology and radiolabeled amino acid uptake measurements were used to functionally characterize the transporter expressed in Xenopus oocytes. hATB(0+) was found to transport both neutral and cationic amino acids, with the highest affinity for hydrophobic amino acids and the lowest affinity for proline. Amino acid transport was Na(+) and Cl(-)-dependent and was attenuated in the presence of 2-aminobicyclo-[2.2.1]-heptane-2-carboxylic acid, a system B(0+) inhibitor. These characteristics are consistent with system B(0+) amino acid transport. Thus, hATB(0+) is the first cloned B(0+) amino acid transporter.

Nutrition and the insulin-like growth factor system

Nutritional status is a key regulator of the circulating and tissue insulin-like growth factor (IGF) system. IGF-I mRNA and protein levels decrease in tissues such as liver and intestine with fasting and are restored with refeeding. Additional studies suggest that the level of protein and calorie intake independently regulate plasma IGF-I concentrations in man. The level of nutrition effects the biological actions of recombinant growth hormone (GH) and IGF-I administration in humans. Limited data demonstrate that plasma and tissue levels of the insulin-like growth factor binding proteins (IGFBPs) are also sensitive to nutrient intake. Specific micronutrients, such as potassium, magnesium and zinc also appear to be important for optimal IGF-I synthesis and anabolic effects in animal models. Malnutrition is common in elderly patients, however, the interaction between specific nutrients, general nutritional status and the aging process on the IGF system is incompletely understood. Mechanisms of nutrient-IGF system interactions which may affect the biological actions of IGF-I, IGF-II, and the IGFBPs are increasingly being determined in basic studies. The effects of underlying nutritional status and responses to dietary intake will be important to evaluate in clinical studies of the IGF system and exogenous growth factor therapy.

The metabolic roles, pharmacology, and toxicology of lysine

L-lysine monohydrochloride (LMH) is widely available to the public as a nonprescription oral supplement. Most of the pharmaceutical-grade product is used as a suppressant of recurrent herpes simplex infections. Recent publications indicate the possibility of other therapeutic uses, e.g., in cardiovascular disease and osteoporosis. These and other potential applications are surveyed and evaluated in this review with suggestions for further study. Data on toxicity are reviewed and recommendations made regarding safety of chronic dosage levels.

Effects of phenylalanine, histidine, and leucine on basal and GHRH-stimulated GH secretion and on PRL, insulin, and glucose levels in short children. Comparison with the effects of arginine

Of the amino acids arginine is the most potent GH secretagogue in man. It potentiates the GH response to GHRH, exerts a weaker PRL-releasing effect, stimulates insulin and glucagon and induces a biphasic glucose variation. The potency and effects of other amino acids on pituitary and pancreatic hormones need to be clarified. In 43 children with normal short stature (5.3-14.0 yr; 30 M and 13 F) the effects of the infusion of phenylalanine (Phe, 0.08 g/kg), histidine (His, 0.1 g/kg), and leucine (Leu, 0.08 g/kg) on basal and GHRH-stimulated GH secretion and on PRL, insulin and glucose levels were studied and compared with those of arginine at high (hArg, 0.5 g/kg) or low dose (lArg, 0.2 g/kg). Phe increased basal (p < 0.05) but not GHRH-stimulated GH levels, induced PRL and insulin rises (p < 0.03 and p < 0.03), and did not change glycemia. Though a trend toward an increase in basal GH levels was found after His, His and Leu did not significantly modify either basal or GHRH-induced GH secretion nor basal PRL, insulin and glucose levels. Both hArg and lArg increased basal (p < 0.0001 and p < 0.05, respectively) and GHRH-stimulated GH levels (p < 0.006 and p < 0.006). hArg increased both PRL (p < 0.002) and insulin levels (p < 0.005) more (p < 0.0005 and p < 0.004) than lArg (p < 0.005 and p < 0.005), while glucose levels showed a similar increase followed by a similar decrease. We conclude that in childhood: a) Phe significantly increases GH secretion but, differently from Arg, does not potentiate the response to GHRH, suggesting different mechanisms of action of these amino acids; b) differently from His and Leu, Phe is a PRL and insulin secretagogue but is less potent than Arg; c) Arg has the highest stimulatory effect on pituitary and pancreatic hormones.

Growth Hormone: Myths and Misconceptions

Growth hormone is one of the many dangerous and illegal ergogenic aids currently used by athletes. In those who suffer from a growth hormone deficiency, supplementation does produce positive results: Muscle volume increases while adipose tissue volume is significantly reduced. Growth hormone supplementation can also lead to strength increases in the deficient population (2, 6, 13) as well as in the elderly population (16, 18, 25). In healthy young men, growth hormone supplementation has been shown to increase fat-free mass and to decrease fat mass. However, these changes are not accompanied by strength gains (5, 7, 23, 24). This finding, coupled with the numerous side effects associated with the drug, presents a strong case for athletes to abandon its use as an ergogenic aid.

The hypotensive effect of L-arginine is associated with increased expired nitric oxide in humans

Endothelial metabolism of L-arginine to L-citrulline and the potent vasodilator, nitric oxide (NO), is important in the regulation of vascular tone and resting BP. L-arginine improves abnormal endothelium-dependent vasodilation in the setting of hypercholesterolemia and has a vasodilatory effect in normal vessels, effects presumed to be mediated through increased endogenous NO production, although this has not been established by direct measurement of NO. In a randomized, placebo-controlled, crossover trial, 10 healthy male subjects received a 30-min infusion of 0.5 g/kg L-arginine hydrochloride. Subjects underwent continuous monitoring of BP and heart rate (HR) as well as intermittent determination of mixed expired NO concentration and plasma L-arginine and L-citrulline levels. Infusion of L-arginine produced a significant fall in mean BP with a peak effect of -9.3 +/- 0.9% (p<0.005). The hemodynamic effects of L-arginine were associated with an increase in mixed expired NO concentration (FeNO) of 55 +/- 15% (p<0.005) from 15 +/- 2 to 21 +/- 3 parts per billion (ppb) and an increase in the rate of pulmonary NO excretion of 118 +/- 45% (p<0.005), as well as a rise in plasma L-citrulline from 25 +/- 4 to 46 +/- 5 micromol/l (p<0.005). There was a significant correlation between the hypotensive response to L-arginine and the increase in expired NO (r=-0.68, p<0.05). The hypotensive effect of L-arginine in humans appears to be mediated, at least in part, by NO synthase metabolism of L-arginine and increased endogenous NO production as indicated both by increased plasma L-citrulline and by increased expired NO.

Metabolic effects of arginine in a healthy elderly population

Recently there has been much interest in the use of arginine to stimulate immune responses and to promote wound healing. In the present study, the effect of an oral supplementation with arginine on the metabolism of 45 healthy, nonsmoking, elderly volunteers was investigated. Subjects were divided into two groups that received either arginine aspartate (17 g free arginine) (n = 30) or a placebo (n = 15). The supplements were taken for a period of 14 days. Dietary intake of food was not controlled. Blood chemistry, lipid profiles, and as an index of nutritional status, serum insulin-like growth factor-1 levels and nitrogen balance were compared before and after supplementation. Two weeks of arginine supplementation led to a significant elevation of serum insulin-like growth factor concentrations and an improved and positive nitrogen balance (2.0 +/- 0.41 g N) when compared with controls (0.11 +/- 0.47 g N; p = 0.0114). In addition the arginine-supplemented group demonstrated a decreased total serum cholesterol with a reduction in the low-density lipoprotein but not the high-density lipoprotein fraction resulting in a increase in the ratio of low- to high-density lipoprotein fraction. No adverse effects were observed at this dosage of arginine. The data suggest that oral arginine supplementation may be used safely in elderly humans.

Glutamate-arginine salts and hormonal responses to exercise

Hormonal changes during exercise is of growing interest because of their role in adaptation, and performance. The production of amino acids (AA) due to the degradation of muscle protein increases during exercise and some AA may be utilized for energy expenditure or as hormonal secretagogues. Thus, one can propose a strategy to reduce muscle protein breakdown and regulate hormones involved in energy metabolism by dietary AA supplementation. We assessed the effects of glutamate-arginine salt (AGs) ingestion on exercise-induced hormonal alterations in highly trained cyclists (age 18-22 yrs). Using an indwelling catheter, we collected multiple blood samples at rest, during warm up, during and after an intense exercise session. Plasma growth hormone (hGH), insulin and cortisol were measured by radioimmunoassay. As reported in previous studies, we observed a marked increase in plasma hGH and cortisol levels during and after exercise in the placebo (Pl) condition as well as a slight decrease in insulin concentration. In addition, we found that the ingestion of AGs had significant effects on some dynamic hormonal changes. AGs had no effect on resting plasma levels of hGH, insulin or cortisol. However, the marked elevation in cortisol and hGH during and after exercise in the placebo condition, was greatly diminished when subjects ingested AGs. Our results show that AGs can modify exercise-induced hormonal changes and raise the possibility that it may be used to alter energy metabolism during endurance exercise.

Low dose orally administered arginine is able to enhance both basal and growth hormone-releasing hormone-induced growth hormone secretion in normal short children

Aim of this study was to verify whether arginine (ARG), which likely inhibits hypothalamic somatostatin release, has an enhancing effect on the GHRH-induced GH rise, even when administered orally at low dose. To this goal we studied the effects of 4 g orally administered ARG, either hydrochloride (ARG-H) or aspartate (ARG-A), on both basal and GHRH (1 microgram/Kg i.v.)-stimulated GH secretion in 31 children with familial short stature (11 males and 20 females, aged 5.5-13.8 yr, pubertal stage I-III, and compared the results with those of i.v. infusion of 0.5 g/kg ARG-H. Oral ARG-H (Group A, n = 11) induced a significant increase of basal GH levels (4.2 +/- 1.3 vs 1.0 +/- 0.4 micrograms/L, p < 0.02) and enhanced the GH response to GHRH (41.1 +/- 8.6 vs 25.3 +/- 6.7 micrograms/L, p < 0.02). Oral ARG-A (Group B, n = 10) induced a slight, but not statistically significant increase in serum GH levels (3.4 +/- 1.5 vs 1.0 +/- 0.3 micrograms/L) and enhanced the GHRH-induced GH rise (49.7 +/- 9.8 vs 26.1 +/- 8.4 micrograms/L, p < 0.05). Intravenous ARG-H (Group C, n = 10) stimulated basal GH levels (6.2 +/- 1.2 vs 1.2 +/- 0.3 micrograms/L, p < 0.005) and increased the GHRH-induced GH rise (46.7 +/- 5.0 vs 17.1 +/- 2.3 micrograms/L, p < 0.005). This response was similar to those after oral ARG-H or ARG-A plus GHRH. No variation was observed in PRL levels after oral ARG (either ARG-H or ARG-A) and/or GHRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the exercise-induced hormone response to branched chain amino acid administration

It was the aim of the present experiment to detect possible effects of branched-chain amino acids (BCAA) on the endocrine response to 1 h of continuous running. Blood samples were collected from 14 long-distance runners (age 24-42 years) in two different trials performed at 1-week intervals. In both trials (E and P) blood samples were collected at the following times: 9 a.m. (basal values sample), 10.30 a.m. (sample 90), 11.30 a.m. (sample 150), 12.30 p.m. (sample 210); the athletes performed 1 h of running at a constant predetermined speed between samples 90 and 150. Following the basal sample a mixture containing BCAA (E trial), or not containing BCAA (P trial) was ingested. In both trials no hormone basal concentrations, except insulin, were changed before exercise. In P trial, following exercise (sample 150), human growth hormone (HGH), prolactin (PRL), adrenocorticotropic hormone (ACTH) and cortisol (C) increased, while testosterone (T) decreased. In sample 210, after 1 h of rest, while ACTH, PRL and HGH had recovered to basal concentrations, C remained elevated and T displayed a further decrease. In the E trial a similar pattern of change was observed in sample 150 for HGH, PRL, ACTH and C; in sample 210 HGH and PRL displayed significantly lower values than in the corresponding P trial samples. The T was not modified by the running exercise and increased during the recovery period. It is, therefore, suggested that BCAA administration before exercise affects the response of some anabolic hormones, mainly HGH and T.