The physiology of growth hormone and sport

Effects of Taekwondo Training on Growth Factors in Normal Korean Children and Adolescents: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

The growth of children and adolescents is both an important health indicator and a major public health issue. Many recent studies have investigated the effects of taekwondo on growth factors, but no consensus has yet been reached. This meta-analysis aimed to determine the effects of taekwondo on the growth factors in children and adolescents (aged 8 to 16 years). Randomized controlled trials from PubMed, Web of Science, Cochrane Library, the Research Information Sharing Service, the Korea Citation Index, and the Korean-studies Information Service System were analyzed. The effect sizes (standardized mean differences, SMD) were calculated, the risk of bias and publication bias were assessed, and the effect size and subgroup analyses were pooled. We found that the taekwondo group had significantly higher levels of growth hormones (SMD 1.78, 95% confidence interval [CI] 0.98-2.58, and p < 0.001) and insulin-like growth factors (SMD 1.76, 95% CI 0.60-2.92, and p < 0.001) than the control group. For height, a medium effect size was observed (SMD 0.62, 95% CI -0.56-1.80, and p = 0.300), but the between-group difference was not significant. Thus, taekwondo had significant positive effects on the secretion of growth hormones and insulin-like growth factors in Korean children and adolescents. A longitudinal follow-up is necessary to determine the effect on height. This suggests that taekwondo can be recommended as an appropriate physical exercise for maintaining normal growth in children and adolescents.

Fatal overdose from injection of human growth hormone; a case report and review of the literature

BACKGROUND

Human growth hormone (HGH) is a categorized as a performance-enhancing substance. HGH has been abused by athletes for doping purposes.

CASE PRESENTATION

We present a first lethal case of HGH acute toxicity. A young-agitated-athlete with a history of somatropin for the past 2-year, who had hallucinations referred to the emergency department reporting to have abused of 300 mg subcutaneous injections of HGH. He was tachycardic with mild hypertension. Lab data revealed hypernatremia (157 mEq/L), hyperkalemia (5.3 mEq/L), high LDH (1448 U/L), and CPK (2620 U/L), in favor of rhabdomyolysis. Routine drug screening tests were negative for all substances. He was intubated due to low O₂ saturation and progressive loss of consciousness. After several episodes of hyperthermia, hypertension, and possibly pulmonary embolism, he died subsequent to somatropin overdose.

CONCLUSIONS

Complications of HGH misuse can be life-threatening and athletes should be warned of its deleterious effects.

Maturity-Associated Variations in Resistance Exercise-Induced Hormonal Responses in Young Male Athletes

PURPOSE

To examine differences in resistance exercise-induced hormonal responses among young athletes according to their maturity levels.

MATERIALS AND METHODS

A total of 12 collegiate and 32 junior high school male athletes were enrolled. The junior high school participants were divided into pre-peak height velocity (PHV) and post-PHV groups, according to their PHV ages. The salivary testosterone, cortisol, and human growth hormone levels were analyzed before (pre), immediately after (post), and at 15 minutes after performing body weight resistance exercise.

RESULTS

The testosterone levels were higher in the collegiate than in the junior high school group (P < .01) and increased after 15 minutes of exercise (P < .01). A significant decrease in the cortisol levels postexercise in the junior high school groups (P < .01) and an increase in the human growth hormone levels at 15 minutes after exercise in the post-PHV group were observed (P < .01). In the collegiate and post-PHV groups, the testosterone-to-cortisol ratio increased post and at 15 minutes after exercise (P < .01). The testosterone-to-cortisol ratio values were higher in the collegiate than in the post-PHV (at preexercise and at 15 min after [P < .01]) and pre-PHV groups (at all times [P < .01]).

CONCLUSION

Exercise-induced acute hormonal responses to resistance exercise may depend on individuals' maturity levels, even in those having the same age.

Serum IGF-I concentrations are low in female bodybuilders in the pre-contest phase

Bodybuilding involves athletes performing a series of poses/postures on the stage so that they can be classified according to their best esthetic and physical appearance during the competition. In the weeks prior to the target competition, the athletes subject themselves to restrictive diets and different physical training methods, as well as using dietary supplementation and, in some cases, anabolic steroids, to reduce body fat to low levels and maintain or increase muscle mass. On the other hand, it is known that physical training is a potent stimulator for releasing the components of the GH/IGF-I axis that are directly linked to the anabolic process. Based on these assumptions, this study aimed to verify the kinetics of IGF-I and of its binding protein IGFBP-3 in female bodybuilders. Serum IGF-I and IGFBP-3 concentrations were recorded before and after standardized training sessions at two different times: in the initial phase (phase 1) and in the final phase of the pre-contest (phase 2) of a 12-week training season. It was possible to conclude that there was a significant reduction in serum IGF-I values at the end of the pre-contest phase that preceded the athletes' participation in a competition. With relation to the serum IGF-I and IGFBP-3 values measured before and after the standardized training session, it was only possible to verify significant changes in the IGF-I values in the initial phase of the pre-contest. It seems reasonable to suggest that the caloric restriction used by bodybuilders may be related to the decrease in IGF-I values verified at the end of the pre-contest phase.

Sleep duration and physical performance during a 6-week military training course

Sleep is vital in influencing effective training adaptations in the military. This study aimed to assess the relationship between sleep and changes in physical performance over 6 weeks of military training. A total of 22 officer-trainees (age: 24 ± 5 years) from the New Zealand Defence Force were used for this prospective cohort study. Participants wore wrist-actigraphs to monitor sleep, completed subjective wellbeing questionnaires weekly, and were tested for: 2.4-km run time-trial, maximum press-up and curl-ups before and after 6 weeks of training. Average sleep duration was calculated over 36 nights (6:10 ± 0:28 hr:min), and sleep duration at the mid-point (6:15 hr:min) was used to stratify the trainees into two quantile groups (UNDERS: 5:51 ± 0:29 hr:min, n = 11) and (OVERS: 6:27 ± 0:09 hr:min, n = 11). There were no significant group × time interactions for 2.4-km run, press-ups or curl-ups (p > .05); however, small effects were observed in favour of OVERS for 2.4-km run (59.8 versus 44.9 s; d = 0.26) and press-ups (4.7 versus 3.2 reps; d = 0.45). Subjective wellbeing scores resulted in a significant group × time interaction (p < .05), with large effect sizes in favour of the OVERS group for Fatigue in Week 1 (d = 0.90) and Week 3 (d = 0.87), and Soreness in Week 3 (d = 1.09) and Week 4 (d = 0.95). Sleeping more than 6:15 hr:min per night over 6 weeks was associated with small benefits to aspects of physical performance, and moderate to large benefits on subjective wellbeing measures when compared with sleeping < 6:15 hr:min.

Sleep and Performance during a Preseason in Elite Rugby Union Athletes

Background: Preseason training optimises adaptations in the physical qualities required in rugby union athletes. Sleep can be compromised during periods of intensified training. Therefore, we investigated the relationship between sleep quantity and changes in physical performance over a preseason phase in professional rugby union athletes. Methods: Twenty-nine professional rugby union athletes (Mean ± SD, age: 23 ± 3 years) had their sleep duration monitored for 3 weeks using wrist actigraphy. Strength and speed were assessed at baseline and at week 3. Aerobic capacity and body composition were assessed at baseline, at week 3 and at week 5. Participants were stratified into 2 groups for analysis: <7 h 30 min sleep per night (LOW, n = 15) and >7 h 30 min sleep per night (HIGH, n = 14). Results: A significant group x time interaction was determined for aerobic capacity (p = 0.02, d = 1.25) at week 3 and for skinfolds at week 3 (p < 0.01, d = 0.58) and at week 5 (p = 0.02, d = 0.92), in favour of the HIGH sleep group. No differences were evident between groups for strength or speed measures (p ≥ 0.05). Conclusion: This study highlights that longer sleep duration during the preseason may assist in enhancing physical qualities including aerobic capacity and body composition in elite rugby union athletes.

The effect of exercise on intramyocellular acetylcarnitine (AcCtn) concentration in adult growth hormone deficiency (GHD)

To cover increasing energy demands during exercise, tricarboxylic cycle (TCA) flux in skeletal muscle is markedly increased, resulting in the increased formation of intramyocellular acetylcarnitine (AcCtn). We hypothesized that reduced substrate availability within the exercising muscle, reflected by a diminished increase of intramyocellular AcCtn concentration during exercise, might be an underlying mechanism for the impaired exercise performance observed in adult patients with growth hormone deficiency (GHD). We aimed at assessing the effect of 2 hours of moderately intense exercise on intramyocellular AcCtn concentrations, measured by proton magnetic resonance spectroscopy (¹H-MRS), in seven adults with GHD compared to seven matched control subjects (CS). Compared to baseline levels AcCtn concentrations significantly increased after 2 hours of exercise, and significantly decreased over the following 24 hours (ANOVA p for effect of time = 0.0023 for all study participants; p = 0.067 for GHD only, p = 0.045 for CS only). AcCtn concentrations at baseline, as well as changes in AcCtn concentrations over time were similar between GHD patients and CS (ANOVA p for group effect = 0.45). There was no interaction between group and time (p = 0.53). Our study suggests that during moderately intense exercise the availability of energy substrate within the exercising muscle is not significantly different in GHD patients compared to CS.

A new action of peptide hormones for survival in a low-nutrient environment

Malnutrition occurs when nutrient intake is too low for any reason and occurs regardless of gender or age. Therefore, besides loss of eating or digestive functionality due to illness, malnutrition can occur when a healthy individual undergoes an extreme diet and biases their nutrition, or when athletes exerts more energy than they can replenish through food. It has recently been reported that in Japan, the mortality rate of leaner individuals is equal to or higher than that of obese people. It is important to understand what homeostatic maintenance mechanism is behind this when the body is under hypotrophic conditions. Such mechanisms are generally endocranially controlled. We address this fundamental concern in this paper by focusing on peptide hormones. We introduce a mechanism for survival in a malnourished state via the regulation of food intake and temperature. Additionally, we will discuss the latest findings and future prospects for research on changes in the endocrine environment associated with malnutrition associated with exercise. We also review changes in next-generation endocrine environments when caused by malnutrition brought on by dieting.

GH Supplementation Effects on Cardiovascular Risk in GH Deficient Adult Patients: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVE

The current meta-analysis aims at evaluating whether the existing clinical evidence may ascertain the effects of growth hormone (GH) replacement therapy on cardiovascular risk, both in isolated GH deficiency (GHD) and in compensated panhypopituitarism including GH deficit.

METHODS

Original articles published from 1991 to 2015 were searched on Medline (Pubmed). Among an overall number of 181 potentially suitable studies, 24 fulfilled the selection criteria and were included in the analysis. Data aggregation was carried out through the calculation of the absolute risk reduction. The meta-analysis was then conducted by means of a fixed-effects model, according to the heterogeneity test (Chi-square statistic).

RESULTS

Fat-free mass (FFM) increase and fat mass (FM) reduction were found, together with a C-LDL reduction, a wide variation in glycaemia and a neutral effect on glycated haemoglobin (HbA1c) and blood pressure. These effects were valid both for isolated GHD patients and for those with compensated panhypopituitarism. The global outcome D showed a nonsignificant reduction of the overall cardiovascular risk (0.53; 95% C.I. -1.23, 2.85).

CONCLUSION

Our meta-analysis shows no signnificatly positive trend in cardiovascular risk after both short and long-term GH supplementation therapy in adult GHD patients. However, a reduction of LDL cholesterol levels has been found. No differences were found between isolated GHD participants and those affected by panhypopituitarism well compensated since at least 3 months.

Testosterone, cortisol, hGH, and IGF-1 levels in an Italian female elite volleyball team

PURPOSE

To assess the transferability of the reference intervals (RI) of testosterone (T), cortisol (C), human growth hormone (hGH), and insulin-like growth factor (IGF)-1, calculated on a normal healthy population, to a population of female elite volleyball players. Secondary aim of this study is the evaluation of the T/C ratio as predictive tool of overtraining during the annual regular season.

METHODS

A retrospective, longitudinal, observational study was performed, enrolling 58 professional female volleyball players periodically evaluated during the regular sportive season, which lasts from September to May.

RESULTS

Statistically significant differences between the volleyball players and reference populations for T (P = .010), C (P < .001), and IGF-1 (P < .001) were found. Three different statistical approaches to calculate the RI in the athlete group showed a high degree of concordance and pointed out a shift upwards of both lower and upper reference limits. The T/C ratio significantly changed among visits (P = .009). In particular, an overall decrease of about 30% was observed for this ratio during the season, suggesting a state of overtraining.

CONCLUSION

T, C, hGH, and IGF-1 reference values calculated on elite volleyball female players are higher than those of the reference population used in normal clinical practice, suggesting that the health status of highly trained subjects needs the definition of tailored RI for these variables. Moreover, the utility of T/C ratio in the evaluation of overtraining is confirmed.

Growth Hormone Improves Cardiopulmonary Capacity and Body Composition in Children With Growth Hormone Deficiency

CONTEXT

Growth hormone deficiency (GHD) in children may be associated with early cardiovascular risk factors and alterations in left ventricular (LV) structure and function; data on cardiopulmonary functional capacity are lacking.

OBJECTIVES

Aim of the study was to evaluate the effect of GHD and growth hormone (GH) therapy on cardiopulmonary functional capacity, left and right cardiac structure and function, and body composition in children and adolescents.

DESIGN

Prospective, case-control study.

PATIENTS AND METHODS

Twenty-one untrained GHD children (11.3 ± 0.8 years) underwent cardiopulmonary exercise testing, echocardiography and dual-energy x-ray absorptiometry, before and after 12 months of GH therapy. Twenty-one controls matched for sex, pubertal status, body mass index, and physical activity (PA) were evaluated at baseline and after 1 year.

RESULTS

At baseline, GHD patients showed reduced LV mass (LVM; 63.32 ± 7.80 vs 80.44 ± 26.29 g/m2, P = 0.006), peak oxygen consumption (VO2peak; 22.92 ± 4.80 vs 27.48 ± 6.71 mL/Kg/min, P = 0.02), peak workload (80.62 ± 29.32 vs 103.76 ± 36.20 W, P = 0.02), and O2 pulse (4.93 ± 1.30 vs 7.67 ± 2.93 mL/beat, P = 0.0003), compared with controls. GHD patients also exhibited lower lean body mass (LBM 65.36 ± 7.84% vs 76.13 ± 8.23%, P < 0.001), and higher fat mass (FM 30.84 ± 7.92% vs 22.19 ± 8.18%, P = 0.001) than controls. GH therapy resulted in a significant increase of LVM (72.01 ± 15.88, P = 0.03), VO2peak (26.80 ± 4.97; P = 0.01), peak workload (103.67 ± 32.24, P = 0.001), O2 pulse (6.64 ± 1.68, P = 0.0007), and LBM (75.36 ± 7.59%, P = 0.0001), with a reduction in FM (22.62 ± 7.73%, P = 0.001). No difference was found in either left or right ventricular function.

CONCLUSION

Our results suggest that cardiac structure, body composition and cardiopulmonary functional capacity are impaired in children with untreated GHD and can be restored after short-term GH replacement therapy.

Targeting GH-1 splicing as a novel pharmacological strategy for growth hormone deficiency type II

Isolated growth hormone deficiency type II (IGHD II) is a rare genetic splicing disorder characterized by reduced growth hormone (GH) secretion and short stature. It is mainly caused by autosomal dominant-negative mutations within the growth hormone gene (GH-1) which results in missplicing at the mRNA level and the subsequent loss of exon 3, producing the 17.5-kDa GH isoform: a mutant and inactive GH protein that reduces the stability and the secretion of the 22-kDa GH isoform, the main biologically active GH form. At present, patients suffering from IGHD II are treated with daily injections of recombinant human GH (rhGH) in order to reach normal height. However, this type of replacement therapy, although effective in terms of growth, does not prevent the toxic effects of the 17.5-kDa mutant on the pituitary gland, which may eventually lead to other hormonal deficiencies. As the severity of the disease inversely correlates with the 17.5-kDa/22-kDa ratio, increasing the inclusion of exon 3 is expected to ameliorate disease symptoms. This review focuses on the recent advances in experimental and therapeutic strategies applicable to treat IGHD II in clinical and preclinical contexts. Several avenues for alternative IGHD II therapy will be discussed including the use of small interfering RNA (siRNA) and short hairpin RNA (shRNA) constructs that specifically target the exon 3-deleted transcripts as well as the application of histone deacetylase inhibitors (HDACi) and antisense oligonucleotides (AONs) to enhance full-length GH-1 transcription, correct GH-1 exon 3 splicing and manipulate GH pathway.

Muscle and skeletal health in children and adolescents with GH deficiency

In addition to promoting linear growth, GH plays a key role in the regulation of bone and muscle development and metabolism. Although GH deficiency is frequently listed among the causes of secondary osteoporosis in children, its impact on bone and muscle health and on fracture risk is still not completely established. Current data suggest that childhood-onset GH deficiency can affect bone and muscle mass and strength, with GH replacement therapy exerting beneficial effects. Moreover, GH withdrawal at final height can result in reduced peak bone and muscle mass, potentially leading to increased fracture risk in adulthood. Thus, the muscle-bone unit in GH deficient subjects should be monitored during childhood and adolescence in order to prevent osteoporosis and increased fracture risk and GH replacement should be tailored to ensure an optimal bone and muscle health.

Doping in sport and exercise: anabolic, ergogenic, health and clinical issues

The use of doping agents is evident within competitive sport in senior and junior age groups, where they are taken by non-elite as well as elite participants. They are also taken in non-sporting contexts by individuals seeking to ‘improve’ their physique through an increase in muscle and/or decrease in fat mass. While attaining accurate data on the prevalence of their use has limitations, studies suggest the illicit use of doping agents by athletes and non-athletes may be 1–5% in the population and greater than 50% in some groups; with the prevalence being higher in males. There is conclusive evidence that some doping agents are anabolic and ergogenic. There is also evidence that the use of doping agents such as anabolic androgenic steroids, growth hormone and other anabolic agents, erythropoietin and stimulants conveys considerable health risks that include, but are not limited to: cardiovascular disease, diabetes, cancer, mental health issues, virilisation in females and the suppression of naturally produced androgens in males. This review will outline the anabolic, ergogenic and health impacts of selected doping agents and methods that may be used in both the sporting and physique development contexts. It also provides a brief tabulated overview of the history of doping and how doping agents may impact upon the analyses of clinical samples.

Growth Hormone Concentrations in Different Body Fluids Before and After Moderate Exercise

BACKGROUND

Growth hormone (GH) has many direct and indirect actions and roles including substrate regulation and priming of some cells of the immune system, and the expected aspects of growth and repair. Different concentrations in human body fluids reflect the exercise-induced growth hormone response (EIGR) after exercise. In populations such as elite athletes, the invasive nature of venous sampling is poorly accepted. Thus, this study examines possible viable alternatives such as urine and saliva samples and the GH concentration.

METHODS

A heterogeneous group of 11 males (age 26.0 ± 5.0 years; body mass 76.5 ± 9.3 kg; VO2peak 57.0 ± 6.0 mL kg-1 min-1) ran for 40 min on a treadmill at 5 % below their individually indentified lactate threshold pace. Samples of urine, saliva and blood were collected immediately pre- and post-test and at 30 and 60 min post-test.

RESULTS

Salivary GH was correlated with serum pre- and post-exercise (p < 0.001); urinary GH was correlated with serum (p < 0.05). However, despite being significantly correlated, it is clear from the large differences in absolute concentration in the three media that the appearance of serum GH due to exercise is different from that of the appearance of salivary and urinary GH. This aspect of compartmental exchanges is very difficult to define and to investigate. Differences in any analyte concentration in different compartments are to be expected between different media, and hence the same medium should be used where the same 'pattern of response' can be tracked.

CONCLUSIONS

The results suggest that urinary and saliva sampling cannot substitute for venous sampling with respect to exercise-induced changes in GH concentration. The use of the analyses in these three areas may be appropriate for further investigation.

The role of zinc dynamics in growth hormone secretion

Human growth hormone (GH) causes a variety of physiological and metabolic effects in humans and plays a pivotal role in postnatal growth. In somatotroph cells of the anterior pituitary, GH is stored in concentrated forms in secretory granules to be rapidly released upon GH-releasing hormone stimulation. During the process of secretory granule biogenesis, self-association of GH occurs in the compartments of the early secretory pathway (endoplasmic reticulum and Golgi complex). Since this process is greatly facilitated by the presence of zinc ions, it is of importance to understand the potential role of zinc transporters that participate in the fine-tuning of zinc homeostasis and dynamics, particularly in the early secretory pathway. Thus, the role of zinc transporters in supplying the secretory pathway with the sufficient amount of zinc required for the biogenesis of GH-containing secretory granules is essential for normal secretion. This report, illustrated by a clinical case report on transient neonatal zinc deficiency, focuses on the role of zinc in GH storage in the secretory granules and highlights the role of specific zinc transporters in the early secretory pathway. © 2013 S. Karger AG, Basel.

Heat acclimation decreases the growth hormone response to acute constant-load exercise in the heat

OBJECTIVE

The major objective of this study was to elucidate the effect of heat acclimation on blood growth hormone (GH) response to moderate intensity exhausting exercise in the heat. In addition, the potential relationship between inter-individual differences in GH response to exercise and variability in exercise-induced sweat loss was investigated.

DESIGN

Twenty young men completed three exercise tests on a treadmill: H1 (walk at 60% VO₂peak until exhaustion at 42 °C), N (walk at 22 °C; duration equal to H1) and H2 (walk until exhaustion at 42 °C after a 10-day heat acclimation program). Core temperature (T(c)) was recorded continuously and venous blood samples were taken before, during and after each exercise test. Exercise-induced sweat production was calculated on the basis of body mass change taking into account water intake and the volume of blood samples drawn.

RESULTS

Lower pre-exercise T(c), lower rate of rise in T(c) during exercise, and prolonged time to exhaustion in H2 compared with H1 revealed that the subjects successfully achieved an acclimated state. Overall, serum GH level was higher in H1 compared with both N and H2 (p<0.001) but did not differ between the two latter trials (p>0.05). T(c) correlated with serum GH concentration (r=0.615, p<0.01). Analysis of the individual data revealed a group (n=9) possessing a threshold-like pattern of the relationship between T(c) and blood GH response, whereas a plateau-like pattern was evident in the rest of the subjects (n=11). Both sweat production (r=0.596; p<0.001) and the rate of sweat production (r=0.457; p<0.001) correlated with the growth hormone area under the curve.

CONCLUSION

Heat acclimation decreases the GH response to moderate intensity exhausting exercise in the heat. GH may have a modest stimulating effect on whole-body sweat production during exercise.

Effects of a Pre-Exercise Meal on Plasma Growth Hormone Response and Fat Oxidation during Walking

The purpose of this study was to determine the effects of a pre-exercise meal on the plasma human growth hormone (hGH) response and fat oxidation during walking. Subjects (n=8) were randomly provided with either 1 g/kg body weight of glucose in 200 mL water (CHO) or 200 mL water alone (CON) 30 min prior to exercise and subsequently walked on a treadmill at 50% of VO2max for 60 min. Plasma hGH concentrations were significantly higher in subjects who received CHO compared to those who received CON at 15 and 30 min. The fat oxidation rate in the CHO was significantly lower than the CON while walking for 5~15, 25~35 and 45~55 min. Plasma FFA levels were also significantly lower in the CHO compared to the CON at 30, 45 and 60 min. Plasma glucose levels in the CHO were significantly lower while plasma insulin levels were significantly higher than in the CON at 15 and 30 min. Therefore, the results of this study suggest that the elevation of plasma hGH levels due to the intake of a pre-exercise meal may not be strongly related to fat oxidation and plasma free fatty acid (FFA) levels during low-intensity exercise.

Estudo do comportamento cortisol, gh e insulina apos uma sessao de exercicio resistido agudo

INTRODUÇÃO: Muitos trabalhos têm estudado o comportamento hormonal nos exercício resistido, entretanto poucos relacionam os hormônios cortisol, GH e insulina. OBJETIVO: Estudar os ajustes das concentrações plasmáticas dos hormônios cortisol, GH e insulina em exercícios resistidos de mesma intensidade com relação à massas musculares distintas. MÉTODOS: Dez voluntários, com 20,3 ± 4,2 anos, 74,1 ± 10,2 kg de peso, 177,2 ± 4,6 cm de estatura e 23,8 ± 3,2 kg/m2 de IMC, realizaram uma sessão de leg press (LP) e supino reto (SR) com quatro séries com 10 repetições a 70% 1 RM com três minutos de intervalo. Foram coletadas amostras de sangue para dosagem das concentrações plasmáticas de cortisol, GH e insulina em repouso (Pré) e em 0' (Rec. 0'), 30' (Rec. 30') e 90' (Rec. 90') de recuperação. RESULTADOS: As concentrações plasmáticas de cortisol foram significativamente reduzidas ao final da recuperação em LP (2,20±0,37 ng/dl para 1,33±0,38ng/dl) em relação à pré-dosagem. As concentrações de GH e insulina elevaram-se significativamente durante a recuperação. GH em LP foi significativamente maior em Rec. 0' (2,75±3,29 ng/ml para 9,60±5,32 ng/dl) do que em pré. A insulina elevou-se significativamente em Rec. 30' em LP (14,70±7,92 ulU/ml para 21,66 ± 8,61 ulU/ml) e em SR (6,17 ± 2,99 ulU/ml para 19,70 ± 13,8 ulU/ml) em relação à pré. As concentrações plasmáticas de insulina pré em LP foram significativamente superiores a SR (14,70 ulU/ml e 6,17 ± 2,99 ulU/ml). CONCLUSÃO: O exercício resistido promoveu diferentes ajustes nas concentrações hormonais de cortisol, GH e insulina durante o período de recuperação.

Characterization and regulation of mechanical loading-induced compensatory muscle hypertrophy

In mammalian systems, skeletal muscle exists in a dynamic state that monitors and regulates the physiological investment in muscle size to meet the current level of functional demand. This review attempts to consolidate current knowledge concerning development of the compensatory hypertrophy that occurs in response to a sustained increase in the mechanical loading of skeletal muscle. Topics covered include: defining and measuring compensatory hypertrophy, experimental models, loading stimulus parameters, acute responses to increased loading, hyperplasia, myofiber-type adaptations, the involvement of satellite cells, mRNA translational control, mechanotransduction, and endocrinology. The authors conclude with their impressions of current knowledge gaps in the field that are ripe for future study.

Detecting growth hormone misuse in athletes

Athletes have been misusing growth hormone (GH) for its anabolic and metabolic effects since the early 1980s, at least a decade before endocrinologists began to treat adults with GH deficiency. Although there is an ongoing debate about whether GH is performance enhancing, recent studies suggest that GH improves strength and sprint capacity, particularly when combined with anabolic steroids. The detection of GH misuse is challenging because it is an endogenous hormone. Two approaches have been developed to detect GH misuse; the first is based on the measurement of pituitary GH isoforms and the ratio of 22-kDa isoform to total GH. The second is based on the measurement of insulin like growth factor-I (IGF-I) and N-terminal propeptide of type III procollagen (P-III-NP) which increase in a dose-dependent manner in response to GH administration. Both methodologies have been approved by the World Anti-Doping Agency (WADA) and have led to the detection of a number of athletes misusing GH.

Decrease in lean body mass in men with prostate cancer receiving androgen deprivation therapy: mechanism and biomarkers

OBJECTIVE

To elucidate the mechanism of the androgen deprivation therapy (ADT)-related decrease in lean body mass (LBM).

MATERIALS AND METHODS

The LBM and blood samples were studied before and after 6 months of ADT in 72 patients with localized prostate cancer. The LBM was assessed using a foot-to-foot bioelectrical impedance analyzer.

RESULTS

Before ADT, the LBM correlated with none of the serum sex steroid levels; however, it correlated closely with serum 5α-androstane-3α,17β-diol glucuronide (Spearman's rank correlation coefficient = 0.409, P = .001) and insulin-like growth factor-1 (IGF-I, Spearman's rank correlation coefficient = 0.329, P = .005). After ADT, the LBM decreased by 0.9% (P = .036), and the serum testosterone and dihydrotestosterone had decreased by 96.8% and 94.3%, respectively (P <.001 for both), and the IGF-I had increased by 11.6% (from 19.9 to 22.2 nmol/L, P = .001). The serum 1,25-dihydroxyvitamin D3 [1,25(OH)2D] levels decreased after ADT by 9.8% (from 66.2 to 59.7 pg/mL, P = .008), and the post-treatment LBM correlated inversely with 1,25(OH)2D (Spearman's rank correlation coefficient = -0.343, P = .003). The post-treatment LBM was dissociated with 5α-androstane-3α,17β-diol glucuronide and IGF-I. The pretreatment and post-treatment LBMs both correlated inversely with serum sex hormone-binding globulin (P = .024 and P = .016, respectively).

CONCLUSION

The deficiency in androgen levels was suggested to be a link to the ADT-related decrease in LBM; the androgen metabolite 5α-androstane-3α,17β-diol glucuronide has a potential value for assessing the LBM in untreated men. IGF-I also promotes muscle building and is positively regulated during ADT. Sex hormone-binding globulin possibly accelerates the ADT-related decrease in LBM. Although the mechanism for the decrease in 1,25(OH)2D and its inverse correlation with LBM during ADT is unclear, 1,25(OH)2D might be a biomarker reflecting the ADT-related decrease in LBM.

GH responses to two consecutive bouts of respiratory muscle endurance training in healthy adults

Repetition of voluntary exercise bouts and of different pharmacological GH-releasing stimuli at 2-h intervals is associated with a complete abolishment of GH responsiveness. By contrast, a different pattern is observed after repeated neuromuscular electrostimulation, which is characterized by preservation of GH responsiveness. Aim of the study was to evaluate GH responses to repeated bouts of respiratory muscle endurance training (RMET) by mean of a specific commercially available device (Spiro Tiger®). Eight healthy men underwent an incremental progressive RMET protocol of 11 daily sessions. Blood samplings for GH, cortisol and lactate (LA) determinations were collected during the 12th session, which was composed of two consecutive bouts of RMET (of identical intensity and duration: 1 min at a respiration rate of 28 acts/min, 5 min at 32 acts/min, 5 min at 34 acts/min, 4 min at 36 acts/min) at a 2 h interval. Baseline GH levels (mean: 0.9±0.4 ng/ml) significantly (p<0.01) increased after the first bout of RMET (peak: 15.7±4.0 ng/ml). The administration of the second bout of RMET resulted in a significantly lower (p<0.05) GH increase (peak: 3.9±0.8 ng/ml) in comparison with the first one. Baseline LA levels (mean: 1.2±0.1 mmol/l) significantly increased (p<0.001) after the first bout of RMET (peak: 2.3±0.2 mmol/l). The administration of the second RMET bout resulted in a comparable LA increase (from a basal value of 1.2±0.1 mmol/l up to a peak of 2.0±0.1 mmol/l, p<0.001). The first bout of RMET caused a significant increase of cortisol levels (p<0.01), starting from a basal mean value of 142.9±9.4 ng/ml up to a peak of 188.8±10.3 ng/ml. By contrast, the second bout of RMET did not induce any significant change of cortisol levels (basal: 149.1±9.0 ng/ml, peak: 168.5±5.1 ng/ml). In conclusion, a single bout of RMET is capable of stimulating GH and cortisol secretions and LA production. When a second bout is repeated after 2 h, there is a blunting of GH and cortisol responses with a preservation of LA release. Further studies are needed to schedule long-term RMET protocols capable of persistently stimulating GH-IGF-I release and to maximally enhance the ergogenic and metabolic benefits of this intervention either in normal subjects (e.g. athletes) or patients with an impairment of motor capabilities requested to perform normal daily activities (i.e. severely obese and elderly people).

The effects of docosahexaenoic acid supplementation and exercise on growth hormone and insulin-like growth factor I serum levels during chronic hypoxia in rats

BACKGROUND

In this study we examined the effects of docosahexaenoic acid (DHA) on growth hormone (GH), insulin-like growth factor I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) in response to chronic hypoxia and exercise training in hypoxic conditions.

METHODS

Thirty-five rats were divided into five groups; control group (C), hypoxia group (H), hypoxia-exercise group (HE), hypoxia-docosahexaenoic acid group (HD), hypoxia-exercise-docosahexaenoic acid group (HED). A treadmill exercise was performed as 30 m/min for 20 min/day, 5 days per week for 28 days at level grade for the exercising groups (HE and HED). DHA was given to the HD and HED groups every day orally (36 mg/kg). The animals, except for the C group, were exposed to hypoxia for 28 days.

RESULTS

Serum levels of GH and IGF-I in the H group decreased after chronic hypoxia (p<0.001). GH and IGF-I in the HD group also decreased compared with the C group (p<0.05, p<0.01, respectively). GH in C group did not show significant difference compared with the HE and HED groups. Decreased serum level of IGF-I was observed for the HED group (p<0.05).

CONCLUSIONS

According to our findings, chronic hypoxia exposure decreases serum levels of GH, and IGF-I and exercise training have a slightly positive effect on GH/IGF-I axis during hypoxia. In addition, DHA supplementation slightly increases GH and IGF-I serum levels in hypoxic conditions. However, this effect on GH/IGF-I axis during hypoxia is not strong compared with exercise. Therefore, we concluded that exercise and/or DHA supplementation does not have additional positive effect on these hormones in hypoxic conditions.

Akt2: a critical regulator of cardiomyocyte survival and metabolism

Akt proteins are serine/threonine protein kinases that participate in several important intracellular signal transduction cascades. Akt1 and Akt2 are expressed in cardiomyocytes, and both are activated by the action of a variety of growth factors and extracellular ligands. In work with genetically modified mice that had targeted disruption of the genes encoding Akt1 or Akt2, findings showed that Akt1 specifically regulated the physiologic growth of cardiomyocytes that occurred in response to exercise training. In contrast, Akt2 does not regulate physiologic growth but instead regulates glucose metabolism in response to insulin stimulation in cardiomyocytes. Furthermore, Akt2 plays a critical role in antagonizing cardiomyocyte apoptosis that occurs in response to a variety of stimuli, including pathologic remodeling after experimental myocardial infarction. In addition, the protein tribbles 3 (TRB3), an Akt antagonist, was found to be expressed in cardiomyocytes and to be induced by stimuli that cause endoplasmic reticulum stress. Endoplasmic reticulum stress-mediated antagonism of Akt signaling in cardiomyocytes was dependent on TRB3 induction. Finally, myocardial infarction caused endoplasmic reticulum stress in the infarct border zone that was associated with TRB3 induction. These results demonstrate the differential roles of Akt family members and the importance of Akt2 in cardiomyocyte survival.

Growth hormone and lactate responses induced by maximal isometric voluntary contractions and whole-body vibrations in healthy subjects

BACKGROUND

In contrast with maximal voluntary resistance exercise, which is allegedly considered a potent GH stimulus in young subjects, evaluation of GH response to whole-body vibrations (WBV) has yielded conflicting results.

METHODS

The acute effects of WBV alone (test A), maximal voluntary isometric contractions (MVC) (test B), and combination of WBV and MVC (test C) on serum GH and blood lactate (LA) levels were studied in 9 healthy adult males. Muscle soreness was assessed 24 and 48 h after exercise by a visual analogue scale.

RESULTS

GH responses were significantly higher after tests B and C than after test A (GH peaks: 18.8 ± 9.5 ng/ml or 20.8 ± 13.7 ng/ml, respectively, vs 4.3 ± 3.5 ng/ml; p<0.05), with no difference between tests B and C. LA concentrations significantly increased after tests A, B, and C, being significantly higher after tests B and C than after test A (LA peaks: 2.0 ± 0.5 mmol/l or 6.7 ± 2.3 mmol/l, respectively, vs 7.6 ± 0.9 mmol/l; p<0.05). Peak LA values were significantly correlated to GH peaks in the 3 tests (r=0.48; p<0.05). Muscle soreness was significantly higher 24-48 h after tests B and C than after test A, no significant differences being present between tests B and C.

CONCLUSIONS

WBV stimulates GH secretion and LA production, with no additive effect when combined with repeated isometric voluntary contractions. Optimization of protocols based on WBV seems important to maximize the positive effects of this intervention on the somatotropic function.

Genetic defects causing functional and structural isolated growth hormone deficiency

Normal somatic growth requires the integrated function of many of the hormonal, metabolic, and other growth factors involved in the hypothalamo-pituitary-somatotrope axis. Human growth hormone (hGH) causes a variety of physiological and metabolic effects in humans and its pivotal role in postnatal growth is undisputed. Disturbances that occur during this process often cause subnormal GH secretion and/or subnormal GH sensitivity/responsiveness resulting in short stature. Despite the complexity of this linear growth process, the growth pattern of children, if evaluated in the context of normal standards, is rather predictable. Children presenting with short stature (i.e out of normal standards) are treated with daily injections of recombinant human GH (rhGH), which leads in almost all cases to an increase of height velocity. Although it is becoming more and more evident that many genes are involved in controlling the regulation of growth, the main aim of this review is to focus on the GH-1 gene, the various gene alterations and their important physiological and pathophysiological role in growth.

Exercise induces a marked increase in plasma follistatin: evidence that follistatin is a contraction-induced hepatokine

Follistatin is a member of the TGF-β super family and inhibits the action of myostatin to regulate skeletal muscle growth. The regulation of follistatin during physical exercise is unclear but may be important because physical activity is a major intervention to prevent age-related sarcopenia. First, healthy subjects performed either bicycle or one-legged knee extensor exercise. Arterial-venous differences were assessed during the one-legged knee extensor experiment. Next, mice performed 1 h of swimming, and the expression of follistatin was examined in various tissues using quantitative PCR. Western blotting assessed follistatin protein content in the liver. IL-6 and epinephrine were investigated as drivers of follistatin secretion. After 3 h of bicycle exercise, plasma follistatin increased 3 h into recovery with a peak of 7-fold. No net release of follistatin could be detected from the exercising limb. In mice performing a bout of swimming exercise, increases in plasma follistatin as well as follistatin mRNA and protein expression in the liver were observed. IL-6 infusion to healthy young men did not affect the follistatin concentration in the circulation. When mice were stimulated with epinephrine, no increase in the hepatic mRNA of follistatin was observed. This is the first study to demonstrate that plasma follistatin is increased during exercise and most likely originates from the liver. These data introduce new perspectives regarding muscle-liver cross talk during exercise and during recovery from exercise.

GH and IGF1 levels are positively associated with musculotendinous collagen expression: experiments in acromegalic and GH deficiency patients

OBJECTIVE

Disproportionate growth of musculoskeletal tissue is a major cause of morbidity in both acromegalic (ACRO) and GH-deficient (GHD) patients. GH/IGF1 is likely to play an important role in the regulation of tendon and muscle collagen. We hypothesized that the local production of collagen is associated with the level of GH/IGF1.

DESIGN AND METHODS

As primary outcomes, collagen mRNA expression and collagen protein fractional synthesis rate (FSR) were determined locally in skeletal muscle and tendon in nine ACRO and nine GHD patients. Moreover, muscle myofibrillar protein synthesis and tendon collagen morphology were determined.

RESULTS AND CONCLUSIONS

Muscle collagen I and III mRNA expression was higher in ACRO patients versus GHD patients (P<0.05), whereas collagen protein FSR did not differ significantly between ACRO and GHD patients in muscle (P=0.21) and tendon (P=0.15). IGF1Ea and IGF1Ec mRNA expression in muscle was higher in ACRO patients versus GHD patients (P<0.01). Muscle IGF1Ea mRNA expression correlated positively with collagen I mRNA expression (P<0.01). Tendon collagen fibrillar area tended to be higher in GHD patients relative to ACRO patients (P=0.07). Thus, we observed a higher expression for collagen and IGF1 mRNA in local musculotendinous tissue in ACRO patients relative to GHD patients. Moreover, there was a tendency towards a higher collagen protein FSR and a smaller collagen fibril diameter in ACRO patients relative to GHD patients. The results indicate a collagen-stimulating role of local IGF1 in human connective tissue and add to the understanding of musculoskeletal pathology in patients with either high or low GH/IGF1 axis activity.

Doping and musculoskeletal system: short-term and long-lasting effects of doping agents

Doping is a problem that has plagued the world of competition and sports for ages. Even before the dawn of Olympic history in ancient Greece, competitors have looked for artificial means to improve athletic performance. Since ancient times, athletes have attempted to gain an unfair competitive advantage through the use of doping substances. A Prohibited List of doping substances and methods banned in sports is published yearly by the World Anti-Doping Agency. Among the substances included are steroidal and peptide hormones and their modulators, stimulants, glucocorticosteroids, β₂-agonists, diuretics and masking agents, narcotics, and cannabinoids. Blood doping, tampering, infusions, and gene doping are examples of prohibited methods indicated on the List. Apart from the unethical aspect of doping, as it abrogates fair-play's principle, it is extremely important to consider the hazards it presents to the health and well-being of athletes. The referred negative effects for the athlete's health have to do, on the one hand, by the high doses of the performance-enhancing agents and on the other hand, by the relentless, superhuman strict training that the elite or amateur athletes put their muscles, bones, and joints. The purpose of this article is to highlight the early and the long-lasting consequences of the doping abuse on bone and muscle metabolism.