Changes in circulating insulin-like growth factor-binding protein-1 (IGFBP-1) during prolonged exercise: effect of carbohydrate feeding.
Plasma levels of glucose, insulin, the insulin-like growth factor (IGF-I and -II) and IGFBP-1 were determined in four young healthy males performing cycle exercise to fatigue while being fed either placebo (trial C) or glucose polymer solution (trial G). There was a significant decline in glucose and insulin from rest to fatigue in C (P < 0.01 and P < 0.05, respectively), but not in G. IGF-I or IGF-II levels did not change significantly in either of the trials. IGFBP-1 levels increased 12-fold in C (11.4 +/- 1.6 ng/ml at rest to 136.5 +/- 19.7 ng/ml at fatigue P < 0.01), and 5.6-fold in G (11.0 +/- 2.3 ng/ml to 62.2 +/- 15 ng/ml, P < 0.05). In C a significant negative correlation was found between IGFBP-1 and glucose (r = 0.69, P < 0.01) and IGFBP-1 and insulin (r = -0.612, P < 0.05) in C, but not in G. These results suggest that during prolonged exercise factors other than insulin or glucose may regulate IGFBP-1 and that IGFBP-1 may serve a role other than to prevent the hypoglycaemic action of the IGFs.
Hopkins
N J
NJ
School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, UK.
Jakeman
P M
PM
Hughes
S C
SC
Holly
J M
JM
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002352:Carrier Proteins / Q000097:blood*; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005221:Fatigue; D005947:Glucose / Q000008:administration & dosage; D006801:Humans; D007328:Insulin / Q000097:blood; D018970:Insulin-Like Growth Factor Binding Protein 1; D007700:Kinetics; D008297:Male; D010919:Placebos; D011108:Polymers
D001786:Blood Glucose; D002352:Carrier Proteins; D004040:Dietary Carbohydrates; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D010919:Placebos; D011108:Polymers; D005947:Glucose