title: IGF-I has no effect on postexercise suppression of the ubiquitin-proteasome system in rat skeletal muscle.
abstract: Both exercise and insulin-like growth factor I (IGF-I) are known to have major hypertrophic effects in skeletal muscle; however, the interactive effect of exogenous IGF-I and exercise on muscle protein turnover or the ubiquitin-proteasome pathway has not been reported. In the present study, we have examined the interaction between endurance exercise training and IGF-I treatment on muscle protein turnover and the ubiquitin-proteasome pathway in the postexercise period. Adult male rats (270-280 g) were randomized to receive 5 consecutive days of progressive treadmill exercise and/or IGF-I treatment (1 mg. kg body wt(-1). day(-1)). Twenty-four hours after the last bout of exercise, the rate of protein breakdown in incubated muscles was significantly reduced compared with that in unexercised rats. This was associated with a significant reduction in the chymotrypsin-like activity of the proteasome and the rate of ubiquitin-proteasome-dependent casein hydrolysis in muscle extracts from exercised compared with unexercised rats. In contrast, the muscle expression of the 20S proteasome subunit beta-1, ubiquitin, and the 14-kDa E2 ubiquitin-conjugating enzyme was not altered by exercise or IGF-I treatment 24 h postexercise. Exercise had no effect on the rates of total mixed muscle protein synthesis in incubated muscles 24 h postexercise. IGF-I treatment had no effect on muscle weights or the rates of protein turnover 24 h after endurance exercise. These results suggest that a suppression of the ubiquitin-proteasome proteolytic pathway after endurance exercise may contribute to the acute postexercise net protein gain.
authors.affiliation: Department of Surgery, Royal North Shore Hospital, University of Sydney, St. Leonards, New South Wales 2065, Australia. akee@cmri.usyd.edu.au
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Kee
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Taylor
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Carlsson
authors.forename: Andre
authors.initials: A
authors.lastname: Sevette
authors.forename: Ross C
authors.initials: RC
authors.lastname: Smith
authors.forename: Martin W
authors.initials: MW
authors.lastname: Thompson
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000737:chemistry / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects / Q000502:physiology; D010447:Peptide Hydrolases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D017207:Rats, Sprague-Dawley; D014020:Tissue Extracts / Q000378:metabolism; D025801:Ubiquitin / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D007328:Insulin; D009097:Multienzyme Complexes; D009124:Muscle Proteins; D014020:Tissue Extracts; D025801:Ubiquitin; D007334:Insulin-Like Growth Factor I; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex