title: Acute exercise attenuates age-associated resistance to insulin-like growth factor I.
abstract: This study examined the influence of acute exercise on the ability of insulin-like growth factor I (IGF-I) to stimulate protein synthesis in an isolated in vitro soleus muscle preparation in female C57Bl/6 mice aged 5, 12, and 24 mo. Gastrocnemius muscles were analyzed for IGF-I receptor mRNA levels, IGF-I receptor number, and IGF-I receptor binding capacities and affinity constants. IGF-I (20 nM) was unable to stimulate rates of protein synthesis in the 12- and 24-mo-old control animals. These animals demonstrated declines in IGF-I receptor protein. After acute exercise, IGF-I receptor mRNA was elevated, IGF-I receptor protein levels were unaffected, and rates of protein synthesis were stimulated by IGF-I in the 12- and 24-mo-old animals. Acute exercise significantly increased IGF-I receptor binding capacity and affinity constants in the 24- but not the 12-mo-old animals. We conclude that acute exercise can restore the action of IGF-I in aged muscle, potentially by increasing the IGF-I receptor binding capacity and affinity or as a result of factors downstream of the IGF-I receptor.
authors.affiliation: Metabolic Biochemistry Laboratory, School of Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: P E
authors.initials: PE
authors.lastname: Willis
authors.forename: S
authors.initials: S
authors.lastname: Chadan
authors.forename: V
authors.initials: V
authors.lastname: Baracos
authors.forename: W S
authors.initials: WS
authors.lastname: Parkhouse
mesh_terms: D000375:Aging; D000818:Animals; D005260:Female; D015870:Gene Expression; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009124:Muscle Proteins / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000378:metabolism*; D005082:Physical Exertion; D012333:RNA, Messenger / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000378:metabolism*
chemical_list: D009124:Muscle Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1