Young elite athletes of different sport disciplines present with an increase in pulsatile secretion of growth hormone compared with non-elite athletes and sedentary subjects

Exercise-induced GH secretion is related to puberty

PURPOSE

Exercise represents a physiological stimulus that initiates the coordinated responses of hypothalamic-pituitary axis and sympathetic nervous system. Aims of the study were: 1) to analyze the response of GH, cortisol and prolactin to acute exercise in healthy children with normal GH response to stimulation tests 2) to evaluate the reliability of physical exercise as a screening test for GH secretion.

METHODS

Forty-four children (mean age 9.35 ± 2.69 years, range 4-13.7) underwent standardized Bruce's test on treadmill. Twenty-nine children were pre-pubertal (nine females and 20 males) and 15 children were pubertal (ten females and five males).

RESULTS

Exercise elicited a peak secretion of all the analyzed hormones. GH showed the highest mean percentage increase (558%), followed by prolactin (178%) and cortisol (23%). In 19/44 children (43.2%), GH peak did not reach the cut-off level of 8 ng/ml, considered as the normal GH response to stimulation tests. Despite a wide inter-individual variability, both GH peak and GH increase from baseline were higher in pubertal children than in pre-pubertal ones (GH peak: 13.49 ± 10.28 ng/ml versus 6.6 ± 4.09 ng/ml-p < 0.001; GH increase: 12.02 ± 10.30 ng/ml versus 5.28 ± 3.97 ng/ml-p < 0.001). The impact of puberty on both GH peak and GH increase was independent of sex, age, BMI SDS and VO₂max. No differences related to sex or pubertal status were found in cortisol and prolactin responses.

CONCLUSION

Exercise-induced GH secretion should not be considered a valuable screening tool in the diagnostic work-up of GH deficiency, due to the wide inter-individual variability in GH response. As described for standard GH stimulation tests, puberty represents the key factor that enhances GH secretion in healthy children.

IGF-I and IGFBP-1 in Relation to Body Composition and Physical Performance in Female Olympic Athletes

INTRODUCTION

Insulin- like growth factor-I (IGF-I) is an anabolic hormone that may affect athletic performance in female athletes, and insulin-like growth factor binding protein-1 (IGFBP-1) is an important regulator of bioactive IGF-I. There is limited knowledge of the role of endogenous IGF-I and IGFBP-1 for body composition and physical performance in female elite athletes.

PURPOSE

To examine IGF-I, age adjusted IGF-I (IGFSD), IGFBP-1 and insulin in female Olympic athletes compared with controls and different sport categories, and in relation to body composition and physical performance in the athletes.

METHODS

Female athletes (n=103) and untrained controls (n=113) were included in this cross-sectional study. Body composition was established by dual-energy X-ray absorptiometry. Serum IGF-I and IGFBP-1 were analyzed by radioimmunoassay and IGFSD was calculated. Insulin was analyzed by electrochemiluminescence immunoassay. Athletes were offered to participate in standardized physical fitness tests.

RESULTS

The athletes demonstrated significantly higher IGF-I, IGFSD and IGFBP-1 and lower insulin levels than controls (p<0.05, p<0.05, p<0.01, p<0.001 respectively). Power athletes had significantly higher IGFSD compared to both endurance and technical athletes (p<0.05, p<0.01, respectively). In athletes and controls combined, significant positive correlations were found between IGF variables and higher bone mineral density (BMD) and lean mass and lower fat percent. IGF-I was positively correlated with squat jump (r_s = 0.28, p<0.05) and IGFBP-1 correlated positively with squats (r_s =0.35, p<0.05).

CONCLUSION

We found higher IGF-I, IGFSD and IGFBP-1 in female athletes than controls, and the highest IGFSD in power athletes. IGF-I and IGFBP-1 were related to increased BMD and lean mass and lower fat percent, as well as were positively associated with physical fitness tests. Future studies are needed to elucidate if these results reflect adaptive responses to physical activity or genetic predisposition.

Laboratory medicine: health evaluation in elite athletes

The need to evaluate the health status of an athlete represents a crucial aim in preventive and protective sports science in order to identify the best diagnostic strategy to improve performance and reduce risks related to physical exercise. In the present review we aim to define the main biochemical and haematological markers that vary significantly during and after sports training to identify risk factors, at competitive and professional levels and to highlight the set up of a specific parameter's panel for elite athletes. Moreover, we also intend to consider additional biomarkers, still under investigation, which could further contribute to laboratory sports medicine and provide reliable data that can be used by athlete's competent staff in order to establish personal attitudes and prevent sports injuries.

Resting Level of Insulin-Like Growth Factor-1 Is Not at Play in Cardiac Enlargement in Endurance-Trained Adolescents

Purpose

The study aimed to investigate resting levels of several selected growth and metabolic hormones in a group of 24 endurance-trained adolescents (aged 13–19 years) compared with 24 untrained age- and sex-matched controls, and to investigate if increased cardiac dimensions were related to these hormones at rest with emphasis on insulin-like growth factor-1 (IGF-1).

Methods

The hormones (cortisol, IGF-1, IGF-2, follicle-stimulating hormone, growth hormone, luteinizing hormone, prolactin, and thyroid-stimulating hormone) were analysed with chemiluminescence microparticle immunoassay (CMIA) or multiplex fluorochrome (Luminex) technique. Cardiac dimensions were assessed by echocardiographic examination at rest. Peak oxygen uptake was obtained by a maximal cardiopulmonary exercise test on a treadmill.

Results

Circulating levels of analysed hormones at rest did not differ between the groups. A correlation was found between increased cardiac dimensions and IGF-1 in the controls, but not in the active group. This correlation declined also among the controls when the cardiac parameters were indexed for body surface area.

Conclusion

Increased cardiac dimensions in endurance-trained adolescents could not be related to resting levels of hormones associated with growth and metabolism, including IGF-1 and GH. In addition, the resting levels of these hormones seem not to be affected by intense regular endurance exercise in adolescents. These findings may contribute to the knowledge about cellular signaling that trigger growth as well as cardiac adaptation to endurance training in young athletes.

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.

Association between exonic polymorphism (rs629849, Gly1619Arg) of IGF2R gene and obesity in Korean population

The aim of this study is to investigate the relationship between single nucleotide polymorphisms (SNPs) and susceptibility to obesity. A previous study suggested that insulin-like growth factors (IGFs) may affect obesity and that IGFs regulate cellular signals by receptors that include the insulin-like growth factor 1 receptor (IGF1R) and the insulin-like growth factor 2 receptor (IGF2R). In this research, the rs3743262 and rs2229765 SNPs of IGF1R gene and rs629849 and rs1805075 SNPs of IG-F2R gene were genotyped in 120 overweight and obese patients with a BMI≥23 kg/m2 (Body Mass Index) and 123 healthy controls with a BMI of 18.5–23.0 kg/m2. Genotyping of each SNP was performed by direct sequencing. Among tested SNPs in IGF1R and IGF2R genes, rs629849 SNP of IGF2R gene showed significant association with obesity (OR=1.86, 95% CI=1.02–3.40, P=0.044 in codominant1 model; OR=1.99, 95% CI=1.10–3.57, P=0.020 in dominant model; OR=1.93, 95% CI=1.13–3.31, P=0.013 in log-additive model). And allele distribution between the control group and overweight/obese group also showed significant difference (OR=1.93, 95% CI=1.14–3.28, P=0.015). In conclusion, these results indicate that rs629849 SNP of IGF2R might be contributed to development of obesity in the Korean population.

Differences in the GH-IGF-I axis in children of different weight and fitness status

OBJECTIVE

To determine if differences in the GH-IGF-I axis exist between children of high and low aerobic fitness who are obese or of normal weight.

DESIGN

124 children (ages 8-11) divided into four groups based on BMI and VO₂max (mL O₂/kg fat free mass(FFM)/min): normal weight--high-fit (NH), normal weight--low-fit (NL), obese--high-fit (OH), and obese--low-fit (OL). Height, weight, skinfolds, body mass index (BMI), body fat percentage and predicted VO₂max (both ml/kg/min and ml/kg(FFM)/min) were assessed. Resting growth hormone (GH), total insulin-like growth factor 1 (total IGF-I), free insulin-like growth factor 1(free IGF-I), and insulin were measured using morning fasting blood samples.

RESULTS

GH was greater in the NH group compared to the OL group only (p<0.01). No group differences existed for either total IGF-I (p=0.53) or free IGF-I (p=0.189). Insulin was greater in the OH and OL groups than the NH and NL groups (p<0.01). With groups combined (or overall), insulin and free IGF-I were related to fitness (insulin--ml/kg/min: r=-0.226, p<0.05 and ml/kg(FFM)/min: r=-0.212, p<0.05; free IGF-I--ml/kg/min: r=-0.219, p<0.01 and ml/kg(FFM)/min: r=-0.272, p<0.05).

CONCLUSIONS

Fitness may contribute to the obesity related reduction of GH that may be involved with weight gain.