The effect of an intravenous infusion of IGF-I and insulin on IGFBP-1, IGFBP-3, acid labile subunit, free and bound IGF-I, catecholamines and potassium in normal volunteers during an amino acid and glucose clamp.
Level 3 - non-randomized controlled study
Small non-randomized controlled physiological clamp study in healthy volunteers
PubMed 9497875 · doi:10.1046/j.1365-2265.1997.3161133.x
What was done
Six healthy human volunteers aged 21 to 49 underwent a 3-hour intravenous infusion of either IGF-I (43.7 pmol/kg/min / 20 mcg/kg/h) or insulin (3.4 pmol/kg/min / 0.5 mU/kg/min) at doses equipotent for hypoglycemic effect during a combined glucose and amino acid clamp. Researchers measured circulating concentrations of total IGF-I, free and bound IGF-I, insulin, IGFBP-1, IGFBP-3, acid labile subunit (ALS), catecholamines (adrenaline and dopamine), and plasma potassium.
What was found
During IGF-I infusion, total IGF-I increased from 26.6 +/- 2.8 to 88.9 +/- 14.2 nmol/l (P < 0.01), insulin decreased from 16.7 +/- 2.9 to 7.2 +/- 1.6 mu/l (P < 0.05), and IGFBP-1 increased over the first 120 minutes from 28.6 +/- 6.3 to 67.9 +/- 10.6 mcg/l (P < 0.05). Free IGF-I and IGF-I bound to 150 and 50 kD fractions also increased significantly (P < 0.05), and plasma potassium decreased from 4.2 +/- 0.06 to 3.56 +/- 0.13 mmol/l (P < 0.05). During insulin infusion, insulin increased from 11.7 +/- 1.6 to 56.7 +/- 16 mu/l (P < 0.01), total IGF-I did not change, IGFBP-1 fell from 27.1 +/- 4.1 to 8.06 +/- 1.6 mcg/l (P < 0.05), and potassium changed from 4.2 +/- 0.07 to 3.92 +/- 0.17 mmol/l. Neither infusion caused significant changes in IGFBP-3, ALS, adrenaline, or dopamine levels.
Why it matters
This study shows distinct acute regulatory actions of IGF-I versus insulin on circulating binding proteins and potassium handling under standardized euglycemic, amino acid-clamped conditions.
Limits
The study was conducted in a very small sample size of only 6 healthy participants. It assessed only acute 3-hour responses under artificial clamped nutrient conditions, and the abstract does not indicate whether treatments were randomized or blinded.
Cited by
- contradicts As insulin levels decrease, levels of IGF-binding protein 3 (IGFBP-3) increase.