Serum levels of insulin-like growth factor-I (IGF-I), and IGF-binding proteins-1 and -3 in middle-aged and young athletes versus sedentary men: relationship with glucose disposal.
The goal of this study was to characterize the respective effects of aging and endurance training on serum insulin-like growth factor I (IGF-I), as well as IGF-binding proteins (IGFBP)-1 and -3 in relationship with glucose disposal. Thirty-two subjects (16 middle-aged men: 8 cyclists and 8 sedentary men; and 16 young men: 8 cyclists and 8 sedentary men) were compared in this study. Insulin sensitivity (SI) and glucose effectiveness (Sg) were assessed by the minimal model. Endurance training increased SI, Sg, and IGFBP-1 and -3 in both age groups (P<.05), but the older group showed a greater increase in SI and IGFBP-1 than the younger group (P<.05). IGF-I was increased only in the middle-aged trained men (P<.05). An effect of aging was found in the sedentary subjects, who presented lower IGF-I and SI (P<.05) when older. This effect disappeared with training since IGF-I and SI were nearly identical in young and middle-aged trained subjects. SI was correlated with IGFBP-1 (P<.01). These data suggest that (1) endurance training increases SI, Sg, and IGFBP-1 and -3 in men and, for SI and IGFBP-1, this increase becomes more pronounced with age; (2) endurance training may attenuate the aged-related decline in SI and IGF-I; and (3) IGFBP-1 may protect against the risk of hypoglycemia by counteracting the hypoglycemic effect of IGF-I in such situations of high SI.
Manetta
J
J
Metabolic Unit, Service Central de Physiologie Clinique, Centre d'Exploration et de Réadaptation des Anomalies Métaboliques et Musculaires, Hôpital Lapeyronie, Monpellier, France.
Brun
J F
JF
Fedou
C
C
Maïmoun
L
L
Prefaut
C
C
Mercier
J
J
D000328:Adult; D000375:Aging; D001642:Bicycling; D001786:Blood Glucose / Q000378:metabolism*; D006801:Humans; D007333:Insulin Resistance; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood*; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D010807:Physical Endurance
D001786:Blood Glucose; D018970:Insulin-Like Growth Factor Binding Protein 1; D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I