Normal spontaneous and stimulated GH levels despite decreased IGF-I concentrations in cystic fibrosis patients

OBJECTIVE: The aim of the present study was to investigate whether patients with cystic fibrosis (CF) are GH resistant with increased GH release and decreased concentrations of IGF-I as a result of malabsorption, increased catabolism and impaired glucose tolerance.

DESIGN: Twenty CF patients were included, ten with normal glucose tolerance (five male, five female, median age 25.5 years (range 20-31)) and ten with diabetes mellitus (five male, five female, median age 25.3 years (range 17-45). Twenty healthy individuals served as controls (ten male, ten female, median age 28.4 years (range 18-36)).

METHODS: GH status was evaluated by 12h spontaneous GH release during the night time, arginine-stimulated GH release and the basal concentrations of IGF-I and insulin-like growth factor-binding protein-3 (IGFBP-3). Twelve hour spontaneous GH profiles were estimated using a constant blood withdrawal technique with sampling every 30min and the Pulsar method was used for the analysis of profiles.

RESULTS: No significant differences were found in spontaneous and stimulated GH release in CF patients compared with healthy controls, whereas IGF-I and IGFBP-3 were significantly decreased in CF patients compared with healthy controls. The combination of reduced IGF-I and IGFBP-3 with normal GH release points to a relative GH resistance or a disturbance in the pituitary axis in patients with CF. The spontaneous GH release, the stimulated GH release and the basal concentrations of IGF-I and IGFBP-3 were not significantly different in diabetic CF patients compared with CF patients with normal glucose tolerance and the presence of diabetes mellitus was not consistent with increased GH resistance in CF patients.

CONCLUSION: CF patients with normal glucose tolerance and diabetic CF patients had normal GH release and decreased concentrations of IGF-I indicating a relative GH resistance.