REPRODUCIBILITY AND COMPARISON OF GROWTH-HORMONE SECRETION TESTS

To assess the degree of reproducibility of spontaneous GH secretion an d pharmacological tests we studied 15 prepubertal children with short stature and abnormal growth rate, In all children, spontaneous overnig ht GH secretion was measured followed by a clonidine test in 8 childre n and an arginine test in the remaining 7. The same protocol was repea ted a week later, Intra-individual variability of GH secretion in both physiological and pharmacological tests was expressed as the coeffici ent of variation (CV%), No significant difference was found between th e first and second value of parameters of spontaneous GH secretion, Ma ximum spontaneous GH peak (MS) and mean 12-h GH concentration (MGH) co rrelated significantly (r=0.78, p<0.001), Mean CV% of all parameters o f repeated GH profiles (around 30%) were lower than those of provocati ve tests (around 70%) (p<0.05). No significant difference was found be tween CV% of clonidine and arginine tests, There was no correlation be tween MGH or MS and GH response to provocative test in the same child. We found a significant correlation between the log transformed maximu m provocative GH response to the arginine test and the length of the t ime interval (in min) from the end of the last GH peak in the previous profile to the time zero of the provocative test (r=-0.60, p<0.05): T his relationship was not found for the clonidine test, We conclude tha t spontaneous GH secretion in children with short stature is more repr oducible than stimulated GH response with a week's difference, Perhaps the higher variability of provocative GH secretion may be related to the state of the endogenous hypothalamic rhythm of both GHRH and somat ostatin release at the time of the test.