Evidence supporting a direct suppressive effect of growth hormone on serum IGFBP-1 levels. Experimental studies in normal, obese and GH-deficient adults.
It has occasionally been suggested that GH directly suppresses circulating IGFBP-1 levels, although it is generally believed that such an effect is secondary to a GH-induced increase in insulin levels. We present data from several experiments in which the effects of GH on IGFBP-1 could be studied more extensively. In normal subjects (n = 36), an i.v. GH bolus caused a small but significant decrease in plasma IGFBP-1 concentrations without changes in insulin [IGFBP-1 (microgram/l): 2.6 +/- 0.3 (GH) vs 3.2 +/- 0.4 (placebo), P < 0.05]. Conversely, a 28-h somatostatin infusion with and without GH administration during fasting in normal subjects yielded higher IGFBP-1 levels in the non-GH substituted study [50.5 +/- 5.3 (GH-suppression) vs 22.6 +/- 5.6 (GH-substitution), P < 0.01], comparable with an increased concentration of IGFBP-1 during fasting in GH-deficient patients without usual GH substitution [23.4 +/- 7.6 (GH pause) vs 14.1 +/- 4.9 (GH substitution), P < 0.01]. In both fasting studies insulin levels remained stable. During a hypocaloric diet, long-term GH treatment in obesity lead to a significant decline in IGFBP-1 level (2.3 +/- 0.6 vs 1.2 +/- 0.2, P < 0.01), while no changes were found in the placebo group. Again, insulin levels remained equally low in both studies. Finally, a significant rebound increase in IGFBP-1 level in response to insulin induced hypoglycemia was only observed among GH-deficient patients, but not in control subjects, the latter of whom responded to hypoglycemia with a significant increase in serum GH levels [23.2 +/- 7.2 (GHDA) vs 2.5 +/- 0.3 (controls), P < 0.01]. In conclusion, a suppressive effect of GH on IGFBP-1 appears to be unmasked in the presence of low or suppressed insulin levels, making GH a potential regulator of IGF-1 bioactivity in a hitherto unrecognized way.
Nørrelund
H
H
Medical Department M (Endocrinology and Diabetes), Aarhus Kommunehospital, Denmark.
Fisker
S
S
Vahl
N
N
Børglum
J
J
Richelsen
B
B
Christiansen
J S
JS
Jørgensen
J O
JO
D000328:Adult; D004038:Diet, Reducing; D004311:Double-Blind Method; D002149:Energy Intake; D005215:Fasting; D005260:Female; D019382:Human Growth Hormone / Q000172:deficiency* / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D007018:Hypopituitarism / Q000097:blood*; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood*; D007700:Kinetics; D008297:Male; D009765:Obesity / Q000097:blood* / Q000628:therapy; D012016:Reference Values; D013997:Time Factors
D018970:Insulin-Like Growth Factor Binding Protein 1; D019382:Human Growth Hormone