Dose-response study of GH effects on circulating IGF-I and IGFBP-3 levels in healthy young men and women

The aim of our study was to define the dose-response effect of a short- term treatment with different recombinant human growth hormone (rhGH) doses (1.25, 2.5, 5.0, 10.0, and 20.0 μg · kg^-1 day^-1 for 4 days) on insulin- like growth factor I (IGF-I) and insulin-like growth factor-binding protein (IGFBP)-3 levels in 21 normal young adults of both sexes. The dose of 1.25 μg/kg rhGH did not modify IGF-I levels. The dose of 2.5 μg/kg rhGH significantly increased IGF-I levels in men (P < 0.05) but not in women, whereas the higher doses increased IGF-I levels in both sexes (P < 0.002). IGFBP-3 levels were not modified by 1.25 or 2.5 μg/kg rhGH in either sex. On the other hand, 5.0 μg/kg increased IGFBP-3 levels in men (P < 0.05) but not in women, whereas the higher doses increased IGFBP-3 levels similarly in both sexes (P < 0.02). In conclusion, our results demonstrate that IGF-I and IGFBP-3 responses to rhGH are dose and sex dependent. However, IGFBP-3 is less sensitive than IGF-I to rhGH stimulation.