Effect of pubertal development and physical activity on plasma ghrelin concentration in boys.

The aim of the present study was to assess the influence of regular physical activity on plasma ghrelin concentration in pre-pubertal and pubertal boys. In addition, the impact of ghrelin concentration on bone mineral density (BMD) was examined. In total, 56 healthy schoolboys aged between 10 and 16 yr were divided into the swimming (no.=28) and the control (no.=28) groups. The subjects were matched by age and body mass index (BMI), generating 9 matched pairs in pubertal group I (Tanner stage 1), 11 pairs in group II (Tanner stages 2 and 3), and 8 pairs in group III (Tanner stages 4 and 5). Swimmers in pubertal groups II and III had significantly (both p<0.05) higher mean ghrelin levels than the controls (group II: 1126.8+/-406.0 vs 868.3+/-411.2 pg/ml; group III: 1105.5+/-337.5 vs 850.8+/-306.0 pg/ml, respectively), whereas no difference was seen in the pubertal group I (1230.8+/-386.0 vs 1272.7+/-424.4 pg/ml). Ghrelin was the most important hormonal determinant for total BMD and lumbar apparent volumetric BMD (BMAD) (R2=27.2% and R2=19.8%, respectively) in swimmers, whereas in control boys, plasma IGF-I was the most important hormonal predictor accounting for 41.8% of the variability of total BMD and 20.4% of the variability of lumbar BMAD. In conclusion, ghrelin concentration decreased during puberty in physically inactive boys, while in regularly physically active boys it remained relatively unchanged. Ghrelin appears to be an important hormonal predictor for BMD in physically active boys, while BMD is mostly determined by IGF-I in physically inactive boys.

Impact of acute exercise on bone turnover and growth hormone/insulin-like growth factor axis in boys.

AIM: The aim of this study was to investigate the response of N-terminal propeptide of type I procollagen, crosslinked telopeptide of type I collagen and the growth hormone/insulin-like growth factor-I axis to acute aerobic exercise in boys at different pubertal stages METHODS: The subjects were 60 healthy boys (group I - Tanner stage 1, N=20; group II - Tanner stages 2 and 3, N=20; group III - Tanner stages 4 and 5, N=20) who exercised 30 minutes at constant load on cycle ergometer at the level of ~95% of their individual ventilatory threshold. Venous blood samples were obtained before, immediately after and after 30 minutes of recovery for the measurement of serum testosterone, growth hormone (GH), insulin-like-growth factor-I, insulin-like-growth factor binding protein-3, N-terminal propeptide of type I procollagen (PINP) and crosslinked telopeptide of type I collagen. RESULTS: Acute exercise did not affect significantly serum testosterone, insulin-like-growth factor-I, insulin-like-growth factor binding protein-3 or bone turnover markers concentrations in any of study groups. The rise in growth hormone concentration during exercise was highest in group III (62.3+/-41.7 mU/L vs 15.5+/-11.4 in group I and 41.8+/-20.0 in group II). The increment in serum growth hormone level during exercise was positively correlated (r=0.64; P<0.001) to basal serum testosterone concentration. CONCLUSIONS: It can be concluded that growth hormone response to exercise was directly dependent on serum testosterone concentration. Acute exercise did not affect serum testosterone, insulin-like-growth factor-I, insulin-like-growth factor binding protein-3 or bone markers levels.

Ghrelin response to acute aerobic exercise in boys at different stages of puberty.

The aim of this study was to investigate the changes in serum ghrelin and leptin concentrations during acute aerobic cycle ergometer test in 60 boys at different pubertal stages. Boys were divided according to their pubertal status as group I (Tanner stage 1, n=20), group II (Tanner stages 2 and 3, n=20) and group 3 (Tanner stages 4 and 5, n=20). Maximal oxygen consumption and individual ventilatory threshold of the subjects were measured directly using stepwise increasing loads on cycle ergometer. Second exercise test consisted of a 30 minute constant load exercise on the same ergometer at the level of approximately 95% of the individual ventilatory threshold. Venous blood samples were obtained before, immediately after and after 30 minutes of recovery for the measurement of serum ghrelin, leptin, testosterone and insulin. At baseline, prepubertal children had significantly higher values for serum ghrelin compared to the groups II and III. Acute exercise altered significantly only insulin concentration. In all the groups, the maximal oxygen consumption/kg correlated positively with basal levels of testosterone (r=0.60, p<0.001) and insulin (r=0.34), and negatively to ghrelin (r=-0.35) and leptin (r=-0.32) (p<0.05). We conclude that moderate acute aerobic exercise does not change serum ghrelin or leptin level in boys at different pubertal stages.

Relationship between ghrelin and anthropometrical, body composition parameters and testosterone levels in boys at different stages of puberty.

The aim of this study was to investigate the relationships between fasting serum ghrelin concentration, anthropometrical and body composition data in boys at different pubertal stages. Sixty healthy non-obese Estonian schoolboys (10 to 18 yr) were divided into 3 groups based on Tanner classification--group I was prepubertal, group II included stages 2 and 3, and group III stages 4 and 5. Additionally, we analyzed subjects as a total group. Fasting ghrelin, leptin, testosterone, insulin and glucose were collected between 08:00 and 10:00 h. Body fat % and lean body mass (LBM) were determined by dual-energy X-ray absorptiometry. Fasting ghrelin decreased, while leptin and insulin did not change and testosterone increased during puberty. There was a negative correlation between serum ghrelin and testosterone concentrations in group II (r=-0.51, p<0.05) and in the total group (r=-0.59, p<0.001). Ghrelin was also related to body height, body mass and LBM in group II and total group also with body mass index in total group. Stepwise multiple regression analysis showed that body height from auxological, LBM from body composition and testosterone from biochemical data explained 38.1, 41.7 and 33.7% of the ghrelin variance in the total group, respectively. In conclusion, body height, LBM and serum testosterone are the major determinants of serum ghrelin among parameters studied. Negative correlation between serum ghrelin and testosterone concentrations indicates that ghrelin may also have a role in male pubertal development.