Mg. Ropelato et al., REPRODUCIBILITY AND COMPARISON OF GROWTH-HORMONE SECRETION TESTS, Journal of pediatric endocrinology & metabolism, 9(1), 1996, pp. 41-50
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.