Effect of two β₂-agonist drugs, salbutamol and broxaterol, on the growth hormone response to exercise in adult patients with asthmatic bronchitis

The aim of our study was to evaluate the effect of the iv administration of two different β₂-receptors agonists, salbutamol and broxaterol, on the growth hormone (GH) response to maximal exercise in 11 patients (8 males and 3 females; age range 18–65 yr; mean±SE age 56±13 yr; BMI 26.2±1.4 kg/m²) with chronic asthmatic bronchitis. All the subjects underwent four cycloergometric exercise tests (incremental workload until maximal predicted heart rate). At baseline, at maximal exercise, at the end of the recovery period and 60 min after the end of each exercise, blood samples were drawn for the assay of GH, glucose, insulin, lactates, norepinephrine and epinephrine. Two exercises were performed without treatment while the remaining two were performed 60 min after the administration of 400 μg of either salbutamol or broxaterol (both diluted in 10 ml of saline) according to a randomized double blind cross-over design. Both exercise tests performed without treatment caused a significant (p<0.05) and similar GH peak with respect to baseline values (from 0.3±0.1 μg/L to 2.8±1.3 μg/L, mean of the two exercise tests). Salbutamol pretreatment blunted the GH response to exercise which caused a no more significant serum GH peak over the baseline levels (from 0.6±0.2 μg/L to 1.4±0.6 μg/L,). Moreover, broxaterol completely abolished the GH response to exercise (baseline level 0.6±0.2 μg/L; peak levels 0.4±0.1 μg/L). The serum GH peak after exercise+broxaterol was significantly (p<0.05) lower as compared to exercise+salbutamol. In conclusion, we have demonstrated for the first time that β₂ stimulation blunts the physiological GH response to maximal exercise in adult human subjects. It can be suggested that changes in brain neurotransmitters, possibly an increase in the alpha-adrenergic tone, are likely to be involved in this endocrine effects of exercise.