FREE AND TOTAL INSULIN-LIKE GROWTH-FACTORS AND INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS DURING 14 DAYS OF GROWTH-HORMONE ADMINISTRATION IN HEALTHY-ADULTS

The objective was to investigate the effect of growth hormone (GH) adm inistration on circulating levers of free insulin-like growth factors (IGFs) in healthy adults. Eight healthy male subjects were given place bo and two doses of GH (3 and 6 IU/m(2) per day) for 14 days in a doub le-blind crossover study. Fasting blood samples were obtained every se cond day. Free TGF-I and IGF-II were determined by ultrfiltration of s erum. Total IGF-I and IGF-II were measured after acid-ethanol extracti on. In addition, GH, insulin, IGF binding protein I (IGFBP-1) and IGFB P-3 were measured, Serum-free and total IGF-I increased in a dose-depe ndent manner during the 14 days of GH administration. After 14 days, s erum-free TGF-I values were 610 +/- 100 ng/l (mean +/- SEM) (placebo), 2760 +/- 190 ng/l (3 IU/m(2)) and 3720 +/- 240 ng/l (6 IU/m(2)) (p = 0.0001 for 3 and 6 IU/m(2) vs placebo; p = 0.004 for 3 IU/m(2) vs 6 IU /m(2)). Total IGF-I values were 190 +/- 10 mu g/l (placebo), 525 +/- 1 0 (3 IU/m(2)), and 655 +/- 40 mu g/l (6 IU/m(2)) (p < 0.0001 tor 3 ana 6 IU/m(2) VS placebo; p = 0.04 for 3 IU/m(2) vs 6 IU/m(2)). There wer e no differences in the levers of free or total IGF-II during the thre e study periods. Insulin-like growth factor binding protein 1 was decr eased during GH administration (p = 0.04 for placebo vs 3 IU/m(2); p = 0.006 for placebo vs 6 IU/m(2)). In conclusion, fasting serum free IG F-I increased dose dependently during GH administration and free IGF-I increased relatively more than total IGF-I. This may partly be due to the decrease in IGFBP-1.