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

OBJECTIVES To investigate the effects of IGF-I and insulin at doses eq uipotent with respect to hypoglycaemic effect on IGF-I concentrations (free and bound), IGF binding proteins, catecholamines and potassium l evels. DESIGN A glucose and amino acid clamp technique was used to inv estigate the effects of a 3h intravenous infusion of either IGF-I 43.7 pmol/kg/min (20 mu g/kg/h) or insulin 3.4 pmol/kg/min (0.5 mU/kg/min) . MEASUREMENTS Circulating levels of total IGF-I, free and bound IGF-I , insulin, IGFBP-1, IGFBP-3, ALS, catecholamines and potassium were me asured. PATIENTS 6 normal human volunteers aged 21-49. RESULTS During the IGF-I infusion, IGF-I levels increased (P<0.01) (26.6 +/- 2.8-88.9 +/- 14.2 nmol/l) and insulin levels fell (P<0.05) (16.7 +/- 2.9-7.2 /- 1.6 mu/l). During the insulin infusion, insulin levels increased (P <0.01) (11.7 +/- 1.6-56.7 +/- 16 mu/l) and there was no change in IGF- I. There was no significant change in IGFBP-3 or ALS during the IGF-I or insulin infusions. There was a significant (P<0.05) fall in IGFBP-1 levels from 27.1 +/- 4.1-8.06 +/- 1.6 mu g/l during the insulin infus ion and a significant (P<0.05) rise during the first 120 min of IGF-I infusion from 28.6 +/- 6.3-67.9 +/- 10.6 mu g/l. There was a significa nt (P<0.05) increase in free IGF-I and IGF-I bound to the 150 and 50 k D plasma fractions during the IGF-I infusion. At basal and the end of the IGF-I infusion adrenaline levels (pmol/l) were: 173 +/- 22 and 174 +/- 28; dopamine levels (pmol/l) were: 415 +/- 87 and 470 +/- 87; pla sma potassium (mmol/l) was 4.2 +/- 0.06 and 3.56 +/- 0.13. At basal an d the end of the insulin infusion adrenaline levels (pmol/l) were: 160 +/- 38 and 163 +/- 21; dopamine levels (pmol/l) were: 238 +/- 26 and 316 +/- 31; plasma potassium (mmol/l) was 4.2 +/- 0.07 and 3.92 +/- 0. 17. There were no significant changes in plasma catecholamine concentr ations with either infusion but potassium concentrations were signific antly (P<0.05) reduced during the IGF-I infusion. CONCLUSIONS We concl ude that an infusion of IGF-I resulted in increased levels of both fre e and bound IGF-I. IGF-I and insulin under conditions of adequate subs trate supply have acute effects on IGFBP-1 and potassium physiology, b ut have little effect on IGFBP-3, ALS or catecholamines.