Exercise and growth hormone: does one affect the other?

Factors affecting height velocity in normal prepubertal children

PURPOSE

To analyze the effects of clinical and laboratory factors, including insulinlike growth factor (IGF) levels, on the height velocity of normal prepubertal children.

METHODS

Ninety-five healthy prepubertal children (33 boys, 62 girls) were enrolled. The mean chronological age was 6.3±1.4 years, with a height standard deviation score (SDS) of -0.88±0.70. IGF-1, IGF binding protein-3 (IGFBP-3), SDS for anthropometric measurements, and changes in SDS for anthropometric measurements were analyzed for 1 year, and their associations with 1-year height velocity were investigated.

RESULTS

The group of children with a 1-year height velocity of ≥6 cm were chronologically younger than the group with a 1-year height velocity of <6 cm (5.9±1.3 years vs. 6.7±1.3 years, P=0.004), with a lesser increase of SDS for body mass index (BMI) over 1 year (-0.18±0.68 vs. 0.13±0.53, P=0.014). There were no differences between the 2 groups in IGF-1 SDS and IGFBP-3 SDS. Multiple linear regression showed that baseline chronological age (r=0.243, P=0.026) and height SDS (r=0.236, P=0.030) were positively associated with IGF-1 SDS. Binomial logistic regression showed that an older chronologic age at referral (odds ratio [OR], 0.68; 95% confidence interval [CI], 0.47-0.99) and an increase of BMI SDS over 1 year (OR, 0.41; 95% CI, 0.18-0.89) were associated with a decreased growth possibility of an above-average height velocity (≥6 cm/yr).

CONCLUSION

Height velocity of normal prepubertal children is affected by an increase of BMI SDS and chronological age. Prepubertal IGF-1 SDS reflects height SDS at the time of measurement but is not associated with subsequent height velocity.

A useful model to compare human and mouse growth hormone gene chromosomal structure, expression and regulation, and immune tolerance of human growth hormone analogues

Human (h) pituitary growth hormone (GH) is both physiologically and clinically important. GH reaches its highest circulatory levels in puberty, where it contributes to energy homeostasis and somatogenic growth. GH also helps to maintain tissues and organs and, thus, health and homeostasis. A reduction in the rate of hGH production begins in middle age but if GH insufficiency occurs this may result in tissue degenerative and metabolic diseases. As a consequence, hGH is prescribed under conditions of GH deficiency and, because of its lipolytic activity, stimulation of hGH release has also been used to treat obesity. However, studies of normal GH production and particularly synthesis versus secretion are not feasible in humans as they require sampling normal pituitaries from living subjects. Furthermore, human (or primate) GH structure and, as such, regulation and potential function, is distinct from non-primate rodent GH. As a result, most information about hGH regulation comes from measurements of secreted levels of GH in humans. Thus, partially humanized hGH transgenic mice, generated containing fragments of human chromosome 17 that include the intact hGH gene locus and many thousands of flanking base pairs as well as the endogenous mouse (m) GH gene provide a potentially useful model. Here we review this mouse model in terms of its ability to allow comparison of hGH versus mGH gene expression, and specifically: (i) GH locus structure as well as regulated and rhythmic expression; (ii) their ability to model a clinical assessment of hGH production in response to overeating and hyperinsulinemia as well as a possible effect of exercise, and (iii) their hGH-related immune tolerance and thus potential for testing hGH-related analogue immunogenicity.

Comparison of performing 12 weeks' resistance training before, after and/or in between aerobic exercise on the hormonal status of aged women: a randomized controlled trial

Background Physiological aging can now be considered as a multi-factorial process that is associated with anatomical and signaling changes associated with endocrine function. The purpose of this study was to investigate the comparison of performing 12 weeks' resistance training before, after and/or in between aerobic exercise on the hormonal status of aged women. Materials and methods Forty healthy aged women (age: 67.35 ± 1.40 years) were randomly divided into three training groups and a control group: resistance followed by endurance training (ER, n = 12), endurance training followed by resistance training (RE, n = 12, interval resistance-endurance (RE) training (INT, n = 12) and a control (Con, n = 12) groups. The training program was done over 12 weeks, 3 times per week. Endurance training was performed on a cycle ergometer (intensity: 60-90% maximum heart rate) and resistance training involved selected resistance exercises (intensity: 40-75 one-repetition maximum, 8-18 repeats). All participants were evaluated before and after the training period. Results and conclusion The data showed that performing resistance training before, after and/or in between aerobic exercise did not influence the adaptive response of insulin like growth factor-1 (IGF-1) (p = 0.07), growth hormone (p = 0.35), cortisol (p = 0.20), insulin (p = 0.72), epinephrine (p = 0.83) and norepinephrine (p = 0.86) levels throughout the study. However, when comparing pre and post, no significant differences were shown following combined training within the SE, ES and INT groups for all variables (p < 0.05), except of IGF-1 within ES (p = 0.04) and SE (p = 0.02), and testosterone within ES (p = 0.007). In conclusion, combined training with RE order may be more effective than other orders for increasing anabolic status in aged women.

Transgenic mice expressing the human growth hormone gene provide a model system to study human growth hormone synthesis and secretion in non-tumor-derived pituitary cells: differential effects of dexamethasone and thyroid hormone

Growth hormone (GH) is regulated by pituitary and hypothalamic factors as well as peripheral endocrine factors including glucocorticoids and thyroid hormone. Studies on human GH are limited largely to the assessment of plasma levels in endocrine disorders. Thus, insight into the regulation of synthesis versus secretion has come mainly from studies done on non-human GH and/or pituitary tumor cells. However, primate and non-primate GH gene loci have differences in their structure and, by extension, regulation. We generated transgenic (171hGH/CS-TG) mice containing the intact hGH1 gene and locus control region, including sequences required for integration-independent and preferential pituitary expression. Here, we show hGH co-localizes with mouse (m) GH in somatotrophs in situ and in primary pituitary cells. Dexamethasone treatment increased hGH and mGH, as well as GH releasing hormone (GHRH) receptor RNA levels, and hGH release was stimulated by GHRH treatment. By contrast, triiodothyronine decreased or had no effect on hGH and mGH production, respectively, and the negative effect on hGH was also seen in the presence of dexamethasone. Thus, 171hGH/CS-TG mouse pituitary cultures represent a model system to investigate hormonal control of hGH synthesis and secretion.

The influence of physical activity on lean mass accrual during adolescence: a longitudinal analysis

During childhood, physical activity is likely the most important modifiable factor for the development of lean mass. However, the effects of normal growth and maturation must be controlled. To distinguish effects of physical activity from normal growth, longitudinal data are required. One hundred nine boys and one hundred thirteen girls, participating in the Saskatchewan Pediatric Bone Mineral Accrual Study, were repeatedly assessed for 6 yr. Age at entry was 8–15 yr. Stature, body mass, and physical activity were assessed biannually. Body composition was assessed annually by dual-energy X-ray absorptiometry. Physical activity was determined using the physical activity questionnaires for children and adolescence. Biological age was defined as years from age of peak height velocity. Data were analyzed using multilevel random-effects models. In boys, it was found that physical activity had a significant time-dependent effect on lean mass accrual of the total body (484.7 ± 157.1 g), arms (69.6 ± 27.2 g), legs (197.7 ± 60.5 g), and trunk (249.1 ± 91.4 g) ( P < 0.05). Although the physical activity effects were similar in the girls (total body: 306.9 ± 96.6 g, arms: 31.4 ± 15.5 g, legs: 162.9 ± 40.0 g, and trunk: 119.6 ± 58.2 g; P < 0.05), boys for the same level of activity accrued, depending on the site, between 21 and 120% more absolute lean mass (g). In conclusion, habitual physical activity had a significant independent influence on the growth of lean body mass during adolescence, once biological maturity and stature were controlled.

Beneficial effects of conjugated linoleic acid and exercise on bone of middle-aged female mice

Conjugated linoleic acids (CLA) are a group of polyunsaturated fatty acids that has recently been shown to have several beneficial effects on different diseases, including prevention of bone loss. The important feature of CLA is to reduce fat mass, thereby reducing body weight significantly. Although loss of body weight is known to increase bone loss, there is increasing evidence that CLA maybe beneficial to bone. Another factor that can reduce body weight is exercise (EX). It is well established that moderate EX stimulates bone formation. In this study, we analyzed the changes in bone using pQCT densitometry in middle-aged C57Bl/6 mice fed CLA (0.5%) and/or exercised. Twelve-month-old mice were divided into the following groups: group 1, corn oil, sedentary (CO SED); group 2, corn oil, exercise (CO EX); group 3, CLA, sedentary (CLA SED); and group 4, CLA, exercise (CLA EX). Mice were maintained in the respective experimental regimens for 10 weeks, after which mice were scanned using DEXA and killed. The lumbar vertebrae, femur, and tibia were analyzed using pQCT densitometry. CLA, when given alone or in combination with EX, significantly reduced body weight and increased lean mass. CLA treatment also significantly increased bone mass. Further, additional increase in bone mass was observed in mice treated with a combination of CLA and EX in almost all the bone sites analyzed. We conclude that CLA, when consumed as a dietary supplement along with moderate treadmill EX, significantly increases bone mass in middle-aged female mice.

Growth hormone 1 (GH1) gene and performance and post-race rectal temperature during the South African Ironman triathlon

BACKGROUND

Some studies have suggested that the insertion allele of the ACE gene is associated with endurance performance, including the Ironman triathlon. It is possible that this association is due to genetic linkage between the ACE I/D locus and the T/A variant in intron 4 of the neighbouring GH1 gene. The A variant is associated with lower levels of growth hormone production. Growth hormone has multiple effects, especially on metabolism during exercise and recovery from exercise. Its production during exercise has also been shown to stimulate sweat rate and heat loss.

OBJECTIVE

To determine whether the GH1 gene is associated with the performance and/or post-race rectal temperatures of competitors in the South African Ironman triathlon.

METHODS

A total of 169 of the fastest finishing white male triathletes who completed the 2000 and/or 2001 South African Ironman triathlon and 155 control subjects were genotyped for the T/A variant in the GH1 gene. Post-race rectal temperature was also determined in 103 of these triathletes.

RESULTS

There was no significant difference in the frequency of this polymorphism in the GH1 gene when the fastest finishing triathletes were compared with the control subjects. Post-race rectal temperatures were, however, significantly higher in those triathletes with an AA genotype (mean (SD) 37.7 (0.8) degrees C) compared with those with a TT genotype (37.2 (0.8) degrees C) (p = 0.019).

CONCLUSIONS

The T/A polymorphism in intron 4 of the GH1 gene was not associated with performance of the fastest finishers of the South African Ironman triathlon. Post-race rectal temperatures were, however, significantly higher in the fastest finishing athletes, who were homozygous for a GH1 genotype associated with lower growth hormone production.

Influence of muscle strength and total work on exercise-induced plasma growth hormone isoforms in women

The purpose of this investigation was to determine the influence of physical strength and the ability to do more total work on human growth hormone (GH) variants to a heavy resistance exercise protocol in untrained women. From a distribution of 100 healthy, untrained women, the strongest 10 women (S) and the weakest 10 women (W) were compared for GH responses pre- and post an acute heavy resistance exercise test (AHRET, 6 sets of 10 RM squats, 2 minutes rest between sets). Blood samples were obtained pre-exercise and immediately post-exercise and subsequently analysed in total as well as fractionated by Sephacryl S-100R column chromatography into three molecular weight size classes: fraction A: > 60 kD, fraction B: 30-60 kD, fraction C: < 30 kD. For each total sample as well as each fraction, immunoreactive GH was measured via the Nichols IRMA, while bioactive GH was measured via the hypox rat tibial line bioassay and Diagnostic Systems Laboratory's immunofunctional GH ELISA. No exercise-induced changes or differences between groups were observed in the tibial line bioassay. However, the S group displayed a significantly higher pre-exercise resting value in the total fraction than the W group. Conversely, the W group exhibited a significantly higher pre-exercise value in the smaller molecular weight fraction C. With regards to the immunofunctional and immunoreactive assays, the total fraction, fraction A, and fraction B demonstrated significant (P < or = 0.05) exercise-induced increases in both the S and W group despite no group differences. For the Nichols and immunofunctional assays significant exercise-induced changes were observed in the smaller molecular weight C fraction in the W group but not the S group. However, the S group displayed a significantly higher pre-exercise value in fraction C relative to the W group. These data demonstrate for the first time that differences exist in the GH molecular weight variants between strong and weak untrained women, with the lower molecular weight variants seemingly less responsive to greater amounts of exercise in stronger women, thus suggesting differential regulation of GH molecular weight variants during resistance exercise due to pre-existing physical parameters.

Growth hormone pulsatility profile characteristics following acute heavy resistance exercise

This investigation examined the hypothesis that acute heavy resistance exercise (AHRE) would increase overnight concentrations of circulating human growth hormone (hGH). Ten men (22 +/- 1 yr, 177 +/- 2 cm, 79 +/- 3 kg, 11 +/- 1% body fat) underwent two overnight blood draws sampled every 10 min from 1700 to 0600: a control and an AHRE condition. The AHRE was conducted from 1500 to 1700 and was a high-volume, multiset exercise bout. Three different immunoassays measured hGH concentrations: the Nichols immunoradiometric assay (Nichols IRMA), National Institute of Diabetes and Digestive and Kidney Diseases radioimmunoassay (NIDDK RIA), and the Diagnostic Systems Laboratory immunofunctional assay (DSL IFA). The Pulsar peak detection system was used to evaluate the pulsatility profile characteristics of hGH. Maximum hGH was lower in the exercise (10.7 microg/l) vs. the control (15.4 microg/l) condition. Mean pulse amplitude was lower in the exercise vs. control condition when measured by the Nichols IRMA and the DSL IFA. A differential pattern of release was also observed after exercise in which hGH was lower in the first half of sleep but higher in the second half. We conclude that AHRE does influence the temporal pattern of overnight hGH pulsatility. Additionally, because of the unique molecular basis of the DSL IFA, this influence does have biological relevance because functionally intact molecules are affected.

Analysis of the effects of growth hormone, exercise and food restriction on cancellous bone in different bone sites in middle-aged female rats

The aim of this study is to determine the effects of growth hormone (GH), exercise (EX), GH+EX and food restriction on cancellous bone in middle-aged female rats. Female F344 rats aged 13 months were divided into (1) age-matched controls; (2) GH treated (2.5 mg/kg. 5 day/week); (3) EX (voluntary wheel running); (4) GH+EX; and (5) food restricted (FR) (fed 60% of the ad libitum food intake). The animals were treated for 18 weeks, at the end of which they were sacrificed. Cancellous bone and cortical bone in the fourth lumbar vertebra, proximal tibial metaphysis (PTM), distal femoral metaphysis (DFM) and femoral neck (NF) were analyzed using peripheral quantitative computerized tomography (pQCT) densitometry. Growth hormone increased cancellous bone area, cancellous bone mineral content, cortical bone area and cortical bone mineral content in the vertebra, PTM, DFM and NF. The tibial muscle wet weight was increased significantly after GH treatment. Exercise increased the cancellous bone area in the vertebra, PTM and DFM. Cortical bone area and cortical bone mineral content increased after EX in the vertebra, PTM, DFM and NF. No significant change was seen in the tibial muscle wet weight after EX. Growth hormone+EX increased cancellous bone area in the vertebra PTM and DFM but had no effect in neck of the femur. Cancellous bone mineral content, cortical bone area and cortical bone mineral content increased with GH+EX in the vertebra, PTM, DFM and NF. The tibial muscle wet weight was increased significantly with GH+EX. Food restriction decreased cancellous bone area and cancellous bone mineral content in all the bones studied. The decrease was statistically significant only at the distal femoral metaphysis. The tibial muscle wet weight decreased when compared with the age-matched control, but this decrease was not statistically significant. We conclude that the effect of the dose of GH used and the levels of voluntary wheel running EX used increased cancellous bone in intact rats; the effect of GH is much greater and different bones respond with varying intensities. The effects of combined treatment of GH and EX on cancellous bone are not always significantly higher than those of GH alone. FR at the level studied has a mostly negative effect on cancellous bone.