Correlation between adrenal function, growth hormone secretion, and insulin sensitivity in children with idiopathic growth hormone deficiency

PURPOSE

Patients with growth hormone deficiency (GHD) demonstrate an increased cortisol/cortisone ratio which could potentially explain the metabolic features of GHD, while GH treatment (GHT) could increase the cortisol metabolism.

METHODS

In 35 children (27 M, mean age 10.1 years) with idiopathic GHD at baseline and after 12 months of GHT and in 25 controls, in addition to metabolic parameters, we assessed adrenal function by morning serum cortisol, its peak, and its area under the curve (AUC_COR) during insulin tolerance test (ITT).

RESULTS

A cortisol peak <18 µg/dl was shown in 22 and 31% of GHD children at baseline and after GHT, respectively. At baseline, GHD children had lower fasting glucose (p < 0.001) and ISI-Matsuda (p = 0.042), with concomitant higher Homa-IR (p = 0.006) and morning cortisol (p = 0.012) than controls. Morning cortisol was negatively correlated with GH (p < 0.001), fasting glucose (p < 0.001) and ISI-Matsuda (p < 0.001) and positively with Homa-IR (p = 0.010). Both cortisol peak and AUC_COR were negatively correlated with GH (all p < 0.001) and ISI-Matsuda (p = 0.016 and p = 0.001, respectively). After 12 months of GHT, a significant increase in fasting glucose (p < 0.001), and Homa-IR (p = 0.011) was documented, with a concomitant decrease in morning cortisol (p = 0.002), AUC_COR (p = 0.038), total (p = 0.003) and LDL-cholesterol (p = 0.016). No significant correlations were found among cortisol levels and all parameters were investigated.

CONCLUSIONS

Cortisol levels correlate with GH secretion and with many metabolic parameters in GHD children, while the metabolic effects during GHT are mainly due to GHT per se and less to cortisol reduction.