Background
The approximate entropy (ApEn) of the secretion of one hormone is a measure of its irregularity of secretion, while cross-approximate entropy (cross-ApEn) assesses the interaction between the secretion of two hormones. The aim was to assess the regularity and interplay of the secretory profiles of leptin (Le), cortisol (F), and growth hormone (GH).
Material and Method
Spontaneous 24-hour Le, F, and GH secretions were analyzed with ApEn and cross-ApEn in 11 short-normal pre-pubertal children (5 boys and 6 girls).
Results
Although the Le, F, and GH levels were not significantly different between the boys and girls, the boys showed more orderly F secretion than the girls, while the latter showed more orderly GH and Le secretions evaluated by ApEn. Moreover, the synchrony between the secretory profiles of Le and the other two hormones as evaluated by cross-ApEn was significantly more regular in the boys.
Conclusions
Differences in the orderliness of secretion of Le, F, and GH were shown between pre-pubertal boys and girls, while increased synchrony was seen between the secretions of Le and GH as well as Le and F in pre-pubertal boys compared with girls. These findings complement the authors' previous research using cross-correlational analyses which demonstrated that the secretory profiles of Le, F, and GH were correlated in time.

Keywords: Leptin - secretion, Hydrocortisone - secretion, Growth Hormone - secretion, Child, Body Height, Radioimmunoassay