Background: End-stage renal failure (ESRF) patients demonstrate augmented growth hormone (GH) secretion, but normal insulin-like growth factor-I (IGF-I) concentrations, indicating a state of GH resistance. To test this hypothesis, we compared the IGF-I response with exogenous GH in haemodialysis patients and healthy controls, with special focus on free GH and bioactive IGF-I.
Methods: Ultrafiltered free GH and total GH were measured in serum collected hourly for 24 h at baseline and after 7 days of recombinant human (rh) GH (50 µg/kg/day) treatment in 11 non-diabetic haemodialysis patients and 10 matched controls. Serum levels of bioactive IGF-I (determined by cell-based IGF-I receptor activation assay), total IGF-I and the GH-binding protein (GHBP) were assayed twice daily.
Results: At baseline, patients showed elevated total GH (24 ± 5 versus 9 ± 1 µg/L × h, P < 0.02), free GH (21 ± 5 versus 7 ± 1 µg/L × h, P < 0.02), reduced GHBP (1.5 ± 0.3 versus 2.5 ± 0.2 nmol/L, P < 0.01), high-normal total IGF-I (173 ± 18 versus 135 ± 14 µg/L, P = 0.12) and subnormal bioactive IGF-I (2.1 ± 0.3 versus 2.8 ± 0.2 µg/L, P < 0.05) when compared with controls. After 7 days of rhGH treatment, there was a greater GH increase in the non-diabetic haemodialysis patients than in controls (total GH: 293 ± 33 versus 166 ± 13 µg/L × h, P < 0.001; free GH: 284 ± 40 versus 126 ± 15 µg/L × h, P < 0.001). GHB remained unaffected and total IGF-I increased to the same extent in patients and controls (701 ± 87 versus 572 ± 33 µg/L, P = 0.17), whereas bioactive IGF-I tended to be lower in patients (5.37 ± 0.55 versus 6.63 ± 0.25 µg/L, P < 0.10). When adjusting for the actual increments in plasma GH, the ability of exogenous GH to stimulate bioactive IGF-I levels was reduced by ~50% in ESRF (P < 0.02), whereas the response of total IGF-I remained normal (74%; P= 0.18)
Conclusions: The study demonstrates that ESRF is associated with markedly elevated serum levels of free GH. Furthermore changes in bioactive, but not immunoreactive, IGF-I indicated that the hepatic sensitivity to GH was reduced by 50% in ESRF patients. Clearly, the physiological importance of our observations awaits further studies, but they suggest that changes in total IGF-I may not necessarily reflect changes in the endogenous activity of IGF-I in ESRF patients on GH treatment.