Acute effect of brief low- and high-intensity exercise on circulating insulin-like growth factor (IGF) I, II, and IGF-binding protein-3 and its proteolysis in young healthy men.
We measured circulating levels of the GH insulin-like growth factor (IGF) system in response to brief exercise of different intensities. Ten males (mean age 28 +/- 5 yr) were studied on three separate occasions: once under resting conditions (control) and once each performing 10 min of low- or high-intensity exercise. Blood samples were assayed by RIA for GH, IGF-I and -II, IGF-binding protein-3 (IGFBP-3), and IGFBP-3 proteolytic activity. After 10 min of low-intensity exercise, IGF-I and IGFBP-3 had increased over preexercise baseline by 7.7 +/- 2.7% (P < 0.05) and 12.5 +/- 3.3% (P < 0.004), respectively. After 10 min of high-intensity exercise, all measured components of the IGF system were increased: IGF-I by 13.3 +/- 3.2% (P < 0.002), IGF-II by 15.7 +/- 3.1 (P < 0.01), and IGFBP-3 by 23 +/- 6% (P < 0.001). IGFBP-3 proteolytic activity also was increased (44 +/- 14% above baseline, P < 0.05). GH reached its peak 10 min after the cessation of high-intensity exercise, unlike the earlier peaks of IGF-I and II. In summary: 1) brief exercise leads to small but significant increases in circulating IGF-I, IGF-II, IGFBP-3, and IGFBP-3 proteolysis; and 2) these responses may be influenced by exercise intensity. The IGF responses seem to be unrelated to GH. Acute exercise-induced proteolysis of IGFBP-3 may contribute to anabolic effects of physical activity by increasing the bioavailability of IGF-I.
Schwarz
A J
AJ
Department of Pediatrics, UCLA Medical Center, Torrance 90509, USA.
Brasel
J A
JA
Hintz
R L
RL
Mohan
S
S
Cooper
D M
DM
D000328:Adult; D015153:Blotting, Western; D010450:Endopeptidases / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D006400:Hematocrit; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D007700:Kinetics; D019344:Lactic Acid / Q000097:blood; D008297:Male; D011863:Radioimmunoassay
D018972:Insulin-Like Growth Factor Binding Protein 3; D019344:Lactic Acid; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D010450:Endopeptidases