Insulin-like growth factor-I in man enhances lipid mobilization and oxidation induced by a growth hormone pulse.
Growth hormone (GH) secretion is suppressed during insulin-like growth factor-I (IGF-I) administration. The aim of the study was to examine whether IGF-I alters the metabolic response to a GH pulse. Seven healthy male subjects (age 27 +/- 4 years, BMI 21.8 +/- 1.7 kg/m2) were treated with NaCl 0.9% (saline) or IGF-I (8 micrograms.kg-1.h-1) for 5 days by continuous subcutaneous infusion in a randomized, crossover fashion while receiving an isocaloric diet (30 kcal.kg-1.day-1). On the third treatment day an intravenous bolus of 0.5 U GH was administered. Forearm muscle metabolism was examined by measuring arterialized and deep venous blood samples, forearm blood flow by occlusion plethysmography and substrate oxidation by indirect calorimetry. IGF-I treatment significantly reduced insulin concentrations by 80% (p < 0.02) and C-peptide levels by 78% (p < 0.02), as assessed by area under the curve. Non-esterified fatty acid (NEFA), glycerol and 3-OH-butyrate levels were elevated and alanine concentration decreased. Forearm blood flow rose from 2.10 +/- 0.43 (saline) to 2.79 +/- 0.37 ml.100ml-1. min-1 (IGF-I) (p < 0.02). GH-pulse: 10 h after i.v. GH injection serum GH peaked at 40.9 +/- 7.4 ng/ml. GH did not influence circulating levels of total IGF-I, C-peptide, insulin or glucose, but caused a further increase in NEFA, glycerol and 3-OH-butyrate levels, indicating enhanced lipolysis and ketogenesis. This effect of GH was much more pronounced during IGF-I: NEFA rose from 702 +/- 267 (saline) and 885 +/- 236 (IGF-I) to 963 +/- 215 (saline) (p < 0.05) and 1815 +/- 586 mumol/l (IGF-I) (p < 0.02), respectively; after 5 h, 3-OH-butyrate rose from 242 +/- 234 (saline) and 340 +/- 280 (IGF-I) to 678 +/- 638 (saline) (p < 0.02) and 1115 +/- 578 mumol/l (IGF-I) (p < 0.02) respectively. After injection of GH, forearm uptake of 3-OH-butyrate was markedly elevated only in the subjects treated with IGF-I: from 44 +/- 195 to 300 +/- 370 after 20 min (p < 0.03) and to 287 +/- 91 nmol.100 ml-1. min-1 after 120 min (p < 0.02). In conclusion, the lipolytic and ketogenic response to GH was grossly enhanced during IGF-I treatment, and utilization of ketone bodies by skeletal muscle was increased.
Bianda
T L
TL
Department of Internal Medicine, University Hospital, Zürich, Switzerland.
Hussain
M A
MA
Keller
A
A
Glatz
Y
Y
Schmitz
O
O
Christiansen
J S
JS
Alberti
K G
KG
Froesch
E R
ER
D000328:Adult; D000409:Alanine / Q000097:blood; D001786:Blood Glucose / Q000032:analysis / Q000378:metabolism; D002096:C-Peptide / Q000097:blood; D018592:Cross-Over Studies; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D005215:Fasting / Q000097:blood; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005542:Forearm / Q000502:physiology; D005990:Glycerol / Q000097:blood; D013006:Growth Hormone / Q000097:blood; D019382:Human Growth Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D006885:Hydroxybutyrates / Q000097:blood / Q000378:metabolism; D007260:Infusion Pumps; D007275:Injections, Intravenous; D007328:Insulin / Q000032:analysis / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D008053:Lipid Mobilization / Q000187:drug effects / Q000502:physiology*; D008066:Lipolysis / Q000187:drug effects / Q000502:physiology*; D008297:Male; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000494:pharmacology
D001786:Blood Glucose; D002096:C-Peptide; D005230:Fatty Acids, Nonesterified; D006885:Hydroxybutyrates; D007328:Insulin; D011994:Recombinant Proteins; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D000409:Alanine; D005990:Glycerol