15 August 2001
Aims: The impact of growth hormone (GH) and prednisolone on the GH/insulin-like growth factor (IGF) axis with special emphasis on IGF binding protein-3 (IGFBP-3) proteolysis was studied in 8 healthy adults in a double-blind cross-over study with four periods: (1) placebo; (2) s.c. GH 0.1 IU/kg/day; (3) oral prednisolone 50 mg/day, and (4) co-administration of GH and prednisolone. Methods: Each treatment period lasted for 4 days followed by a washout period of 10 days. We measured IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3 by immunoassays, IGFBP-3 by Western ligand blotting (WLB) and finally in vitro IGFBP-3 proteolysis by a <sup>125</sup>I-IGFBP-3 degradation assay. Results: IGF-I levels increased by 99% during GH administration and 67% during co-administration of GH and prednisolone (p < 0.0005), whereas no significant change was seen during prednisolone alone. IGFBP-1 levels decreased 55% during the prednisolone period (p < 0.002), but the between period changes were not significant (p < 0.1). IGFBP-2 decreased 33% during co-administration of GH and prednisolone (p < 0.002). IGFBP-3 increased 12% during GH and 7% during co-administration of GH and prednisolone (p < 0.003 and p < 0.03 compared to placebo, respectively), whereas prednisolone alone induced no significant changes. IGFBP-3 measured by WLB did not change significantly, neither did IGFBP-3 proteolysis. Conclusions: Prednisolone administration induces only minimal changes in circulating components of the IGF axis and is not accompanied by alterations in IGFBP-3 proteolysis. This indicates that the metabolic effects of glucocorticoids do not depend on serum IGF-I.