Role of insulin and IGF-I in activation of muscle protein synthesis after oral feeding.
The aim was to evaluate the role of insulin and insulin-like growth factor I (IGF-I) in activation of muscle protein synthesis after oral feeding. Synthesis rate of globular and myofibrillar proteins in muscle tissue was quantified by a flooding dose of radioactive phenylalanine. Muscle tissue expression of IGF-I mRNA was measured. Normal (C57 Bl) and diabetic mice (type I and type II) were subjected to an overnight fast (18 h) with subsequent refeeding procedures for 3 h with either oral chow intake or provision of insulin, IGF-I, glucose, and amino acids. Anti-insulin and anti-IGF-I were provided intraperitoneally before oral refeeding in some experiments. An overnight fast reduced synthesis of both globular (38 +/- 3%) and myofibrillar proteins (54 +/- 3%) in skeletal muscles, which was reversed by oral refeeding. Muscle protein synthesis, after starvation/ refeeding, was proportional and similar to changes in skeletal muscle IGF-I mRNA expression. Diabetic mice responded quantitatively similarly to starvation/refeeding in muscle protein synthesis compared with normal mice (C57 Bl). Both anti-insulin and anti-IGF-I attenuated significantly the stimulation of muscle protein synthesis in response to oral feeding, whereas exogenous provision of either insulin or IGF-I to overnight-starved and freely fed mice did not clearly stimulate protein synthesis in skeletal muscles. Our results support the suggestion that insulin and IGF-I either induce or facilitate the protein synthesis machinery in skeletal muscles rather than exerting a true stimulation of the biosynthetic process during feeding.
Svanberg
E
E
Department of Surgery and Internal Medicine, Sahlgrenska University Hospital, University of Göteborg, Sweden.
Zachrisson
H
H
Ohlsson
C
C
Iresjö
B M
BM
Lundholm
K G
KG
D000821:Animal Feed; D000818:Animals; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000503:physiopathology; D004435:Eating; D005260:Female; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D009124:Muscle Proteins / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000378:metabolism; D012016:Reference Values; D013217:Starvation / Q000503:physiopathology
D007328:Insulin; D009124:Muscle Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I