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Several studies have demonstrated that the obesity-related hyposomatropism is usually reversible after a consistent weight loss induced by diet and/or bariatric surgery. Recently, a single bout of respiratory muscle endurance training (RMET) by means of a specific commercially available device (Spiro Tiger®) has been reported to induce a marked GH response in obese adults, its GH-releasing effect being significantly lower in obese adolescents. The GH response disappeared in both obese adults and adolescents when RMET was repeated at 2-h intervals in-between. The aim of the present study was to evaluate GH responses to repeated bouts of RMET administered before and after a 3-week in-hospital multidisciplinary body weight reduction program (entailing energy-restricted diet, 90 min/daily aerobic physical activity, psychological counseling, and nutritional education) combined with a progressively increasing RMET (15 daily sessions, 5 sessions per week) in 7 obese male adolescents [age: 12-17 years; body mass index (BMI): 38.5±3.1 kg/m2; percent fat mass (FM): 37.0±2.0%]. Blood samplings for GH determinations were collected during the 1st and 15th sessions, which were composed of 2 consecutive bouts of RMET (of identical intensity and duration) at 2-h interval in-between. At the beginning of the study, baseline GH levels significantly increased after the first bout of RMET in all subjects (p0.05). The administration of the second bout of RMET resulted in a significantly lower (p0.05) GH increase in comparison with the first one. Three weeks of the integrated intervention significantly reduced both body weight (from 115.3±9.2 kg to 111.5±8.7 kg, p0.05) and FM (from 43.1±5.7 kg to 41.9±5.3 kg, p0.05), these combined effects being, however, not sufficient to influence GH responsiveness to the 2 repeated bouts of RMET (GH peaks to the first bout: 4.8±1.6 ng/ml vs. 4.8±1.6 ng/ml; GH peaks to the second bout: 0.9±0.2 ng/ml vs. 1.1±0.1 ng/ml, before and after 3 weeks of the treatment, respectively, p=NS). In conclusion, a 3-week incremental RMET combined with a body weight reduction intervention does not seem useful to positively influence the reduced GH responsiveness to 2 repeated RMET bouts in obese adolescents. More intensive and/or long-term RMET protocols, associated with energy-restricted diets, determining more consistent changes in body composition, are likely needed to restore the impaired GH-IGF-1 function of obese adolescents.

Repeated bouts of GH-releasing stimuli (both pharmacological and physiological, such as aerobic exercise) at 2-h intervals are associated with a blunting of somatotropic responsiveness in normal adults, while a persistent GH responsiveness to consecutive stimuli is reported to occur in children and adolescents. Recently, a single bout of respiratory muscle endurance training (RMET) by means of a specific commercially available device (Spiro Tiger®) has been shown to induce relevant GH responses in both normal-weighted and obese adult subjects. The aim of the present study was to evaluate GH responses to repeated bouts of RMET in obese adolescents and adults. Seven obese male adolescents (age: 15.7±0.4 years; body mass index, BMI: 38.0±3.3 kg/m2) and 10 obese adults (age: 22.2±1.4 years; BMI: 39.9±1.0 kg/m2) underwent an incremental progressive RMET protocol of 11 daily sessions. Blood samplings for GH determinations were collected during the 12th session, which was composed of 2 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 in-between. Baseline GH levels significantly increased after the first bout of RMET in all subjects, higher GH peaks being found in obese adults than in obese adolescents (peaks: 14.3±2.1 ng/ml vs. 4.8±1.6 ng/ml, respectively, p

Myostatin and mechano-growth factor (MGF), an isoform of insulin-like growth factor-I (IGF-I), are two important regulators of muscle hypertrophy. The aim of the present study was to investigate the effects of recombinant human growth hormone (rhGH) and/or testosterone on muscle MGF/IGF-IEa/myostatin expression in intact and hypophysectomized rats treated for 15 d with 1) saline or rhGH, 2) sesame oil or testosterone, 3) saline+sesame oil, or rhGH+testosterone (first experiment) or for 7 d with saline or rhGH (second experiment). Animals were killed by decapitation 24 h or 4 d after the last injection (first or second experiment, respectively). Muscle expressions of MGF, IGF-IEa, and myostatin were determined by RT-PCR. A significant increase in the weight of gastrocnemius muscle was observed only in hypophysectomized rats treated with rhGH alone or in combination with testosterone. Administration of rhGH to hypophysectomized rats caused a marked increase in both MGF and IGF-IEa muscle mRNA levels (without any change in the muscle expression of myostatin), an effect that was abolished when testosterone was combined with rhGH. Conversely, in intact rats rhGH increased myostatin muscle mRNA levels without affecting those of MGF and IGF-IEa. Testosterone, alone or combined with rhGH, induced an inhibition of myostatin expression in the muscle of intact rats, but did not change muscle paradigms of hypophysectomized rats. In conclusion, rhGH and/or testosterone anabolic effects in the muscle are mediated by a different expression of MGF/IGF-IEa/myostatin, which is related to the pituitary function.