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      No Influence of Prednisolone on IGFBP-3 Proteolysis in Healthy Young Men

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          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.

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          Most cited references 3

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          Glucocorticoids and muscle catabolism.

          Glucocorticoids inhibit protein synthesis and stimulate protein degradation in skeletal muscle and are an important factor in the development of muscle atrophy in various catabolic conditions. Glucocorticoid-stimulated muscle protein breakdown is primarily caused by ubiquitin-proteasome-dependent proteolysis although calcium-dependent protein degradation may also be involved. In certain catabolic conditions, including sepsis, an interaction between glucocorticoids and proinflammatory cytokines is important for the stimulation of muscle protein breakdown.
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            Differential Changes in Free and Total Insulin-Like Growth Factor I after Major, Elective Abdominal Surgery: The Possible Role of Insulin-Like Growth Factor-Binding Protein-3 Proteolysis

             C. Skjarbak (1998)
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              The pharmacokinetics of free insulin-like growth factor-I in healthy subjects.

              In a randomized cross-over study in five healthy males we compared 75-min constant i.v. infusion of saline, low-dose recombinant human (rh) insulin-like growth factor-I (rhIGF-I; 1.5 microg/kg/h) and high-dose rhIGF-I (9.0 microg/kg/h). Serum samples were analysed for ultrafiltered free IGF-I (fIGF-I), total IGF-I (tIGF-I), tIGF-II and IGF-binding protein-1 (IGFBP-1) and -3. Free and total IGF-I were unchanged during saline infusion. Low-dose rhIGF-I caused a small increment in fIGF-I [+41%, from 0.64 +/- 0.19 (mean +/- SEM) to 0.90 +/- 0.25 microg/l;P< 0.05] and tIGF-I (+9%, from 220 +/- 31 to 239 +/- 33 microg/l;P< 0.05). High-dose rhIGF-I increased tIGF-I by 40% (from 227 +/- 36 to 329 +/- 31 microg/l;P< 0.05), and fIGF-I by 11.5 times (from 0.56 +/- 0.20 to 6.46 +/- 1.39 microg/l;P< 0.05). The pharmacokinetic profile of fIGF-I was calculated after high-dose IGF-I only. The disappearance of fIGF-I followed first order kinetics with an apparent half-life of 14.4 +/- 1.0 [11.2-17.1 (range)] min. The clearance was estimated to 52 +/- 20 (16-128) ml/min/kg and the volume of distribution to 1102 +/- 464 (388-2899) ml/kg. In the three experiments, there were no differences in IGFBP-1, and tIGF-II and IGFBP-3 remained unchanged. In conclusion, fIGF-I remained within the physiological range after low-dose rhIGF-I, whereas high-dose rhIGF-I resulted in supraphysiological concentrations. Since the half-life estimates for each subject were remarkably similar, this parameter most likely does not explain the observed variation in clearance and volume of distribution of fIGF-I. Instead, differences in the circulating and cellular IGF-I binding capacity may be of importance.

                Author and article information

                Horm Res Paediatr
                Hormone Research in Paediatrics
                S. Karger AG
                15 August 2001
                : 55
                : 2
                : 95-101
                aMedical Department M, Aarhus Kommunehospital; bInstitute of Experimental Clinical Research, Aarhus University, and cMedical Department V, Aarhus Kommunehospital, Aarhus C, Denmark
                49977 Horm Res 2001;55:95–101
                © 2001 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 1, References: 46, Pages: 7
                Original Paper


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