The effect of submaximal exercise on immuno- and bioassayable IGF-I activity in patients with GH-deficiency and healthy subjects.
OBJECTIVE
Growth hormone (GH) increases during exercise, but the response of the insulin-like growth factor (IGF) system has not been as definitive. Therefore, we investigated the effect of the exercise-induced GH response on the circulating IGF-system in GH-deficient (GHD) and intact adults.


METHODS
Eight GHD adults were studied on 2 occasions, with (+GH) and without (-GH) GH administered (0.4 IU) during exercise (45 min of cycle ergometer exercise at the lactate threshold). Eight age-matched controls were only studied on one occasion. Blood samples were drawn at baseline, during and post-exercise. IGFBP-3 proteolysis was measured by an in vitro proteolytic activity assay, IGF-I bioactivity by novel IGF-I kinase receptor activation assay (KIRA) and other hormones by immunoassay.


RESULTS
GH administration to GHD adults resulted in a serum GH peak similar to the exercise-stimulated GH response in GH intact controls, but exercise had only a small impact on the IGF system. IGF-I concentration was lower in controls but was only significantly lower than the +GH day. Neither IGF-I nor -II levels changed over time. IGFBP-1 demonstrated a time effect (P<0.01) in all groups, and a time x group interaction (P<0.01) with a rise at 75 min post-exercise, which was greater in the GHD subjects than controls. IGFBP-2 and -3 increased significantly (P<0.01) over time in the GHD subjects, but not in the controls. No change in IGFBP-3 proteolysis or IGF-I bioactivity was found during exercise or recovery in either group.


CONCLUSIONS
Submaximal exercise induced minor changes in IGFBP-1, -2 and -3, without affecting IGFBP-3 proteolysis and IGF-I bioavailability. Thus the metabolic status during submaximal exercise does not require a change in plasma IGF-I bioavailability. Administration of GH to GHD adults does not result in changes in proteolysis or bioavailability.
Kanaley
J A
JA
Department of Exercise Science, Syracuse University, 820 Comstock Avenue, Room 201, Syracuse, NY 13244, USA. jakanale@syr.edu
Frystyk
J
J
Møller
N
N
Dall
R
R
Chen
J-W
JW
Nielsen
Sven C
SC
Christiansen
J S
JS
Jørgensen
J O L
JO
Flyvbjerg
A
A
D000328:Adult; D001682:Biological Availability; D015444:Exercise; D019382:Human Growth Hormone / Q000172:deficiency*; D006801:Humans; D007118:Immunoassay; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000378:metabolism; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D017526:Receptor, IGF Type 1 / Q000378:metabolism
D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1