Exercise-induced GH secretion is related to puberty.

ABSTRACT

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.