Effect of growth hormone deficiency and recombinant hGH (rhGH) replacement on the hypothalamic-pituitary-adrenal axis in children with idiopathic isolated GH deficiency

Objective: Recombinant hGH (rhGH) therapy may unmask central hypoadrenalism in adults with organic GH deficiency (GHD), likely by normalizing 11β-hydroxysteroid dehydrogenase type 1 isoenzyme (11βHSD1) activity and reducing cortisone to cortisol conversion. The aim of the present study was to evaluate the hypothalamic-pituitary-adrenal (HPA) axis in children with idiopathic isolated GHD and normal pituitary magnetic resonance imaging (MRI) both before and during rhGH therapy. Design and patients: This was a single-centre study of 10 consecutive children [five males and five females, mean age: 12.2 ± 1.0 year]. Evaluation was performed at baseline and on rhGH (mean duration: 10.9 ± 2.9 months, mean dose: 0.030 ± 0.002 mg/kg bw/day). Measurements: HPA function was assessed by serum cortisol levels before and after appropriate provocative stimuli, that is, 1 μg ACTH test (N = 5 patients) or insulin tolerance test (ITT, N = 5 patients), evaluating all children with the same stimulation test both before and during rhGH therapy. Central hypoadrenalism was excluded by the presence of either a peak of > 500 nmol/l or a rise in cortisol levels of > 200 nmol/l, after both tests. Results: On rhGH therapy, serum IGF-I levels normalized, while serum cortisol and ACTH levels did not significantly differ from those recorded at baseline. The mean serum cortisol peak after both provocative tests was not significantly different on rhGH therapy and at baseline (498 ± 41 vs. 580 ± 35 nmol/l, respectively, P = 0.06), the mean cortisol rise being 280 ± 45 and 270 ± 36 nmol/l on rhGH and at baseline, respectively. Conclusions: According to the diagnostic criteria, no child became hypoadrenal on rhGH, contrary to what observed in patients with organic GHD, further supporting the view that only in patients with organic multiple pituitary hormone deficiency GHD masks the presence of a hidden central hypoadrenalism.