ABSTRACT
OBJECTIVE: A positive correlation between 24-h spontaneous growth hormone (GH) and cortisol secretion was previously reported in children. This observation prompted us to examine the relationship between physiological diurnal cortisol variation and the levels of insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) under physiological conditions. DESIGN AND PATIENTS: Starting at 0800 h, blood was sampled every 20 minutes over 24 h for measurement of GH and cortisol concentration in nine non-GH- deficient boys as part of a protocol for the investigation of short stature. MEASUREMENTS: IGFBP-1 and insulin were measured in samples drawn every 4 h over the 24-h period while IGF-I, IGF-II, IGFBP-2 and IGFBP-3 were determined in samples collected at the end of the study. RESULTS: No correlation was observed between IGF-I or IGF-II and mean cortisol levels. IGFBP-1 concentrations showed a marked circadian variation that was superimposed on the circadian rhythm for cortisol while a significant positive correlation was found for single point measurements between IGFBP-1 concentrations and cortisol levels measured in the same sample (r = 0.53) or at the preceding 20 minutes (r = 0.43), 40 minutes (r = 0.47) and 2 h (r = 0.38), suggesting an interplay between cortisol and IGFBP-1. A negative correlation (r = - 0.54) was found between IGFBP-1 and insulin levels determined in the same sample. A negative correlation (r = - 0.93) was also found between IGFBP-2 levels and mean cortisol concentrations during the preceding 12 h. No correlation was observed between plasma IGFBP-3 measured by IRMA and mean cortisol levels. CONCLUSION: Our data indicate a clear correlation between cortisol and IGFBP-1 and IGFBP-2 levels. Thus, the interplay of spontaneous GH and cortisol secretion in children may involve changes in IGFBP-1 and IGFBP-2 levels.