Insulin-like growth factor I inhibits degradation and improves retention of protein in hindlimb muscle of lambs.
We infused recombinant human insulin-like growth factor I (IGF-I) for 4 h at 12.3 micrograms.h-1.kg live weight-1 directly into the left femoral artery and measured the rates of synthesis, degradation, and gain of protein by the treated and contralateral limbs of well-fed (n = 8), feed-restricted (n = 10), and fasted (n = 9) castrated male lambs. Reducing feed intake decreased net protein gain of hindlimb muscle, reduced hindlimb glucose uptake, and lowered arterial plasma concentrations of IGF-I, insulin, glucose, phenylalanine, tyrosine, and isoleucine. The effect of nutrition on IGF-binding proteins (IGFBP) was generally small; IGFBP-2 was more abundant in fasted lambs. Infusion of IGF-I into the left femoral artery increased plasma levels of IGF-I 2- to 4-fold in the left femoral vein and by 1.5- to 3-fold in the artery and right femoral vein. In the treated limb, IGF-I reduced protein degradation, increased protein gain, and increased glucose uptake without altering blood flow or oxygen uptake, regardless of feed intake. Systemically, IGF-I reduced plasma insulin, phenylalanine, tyrosine, isoleucine, and leucine in all nutrition groups. Plasma IGFBP-3 was increased by 4 h of IGF-I treatment in fasted but not in fed lambs. In fed but not fasted lambs, IGF-I increased blood glucose concentration. Effects of IGF-I on protein metabolism in the contralateral limb were affected by nutrition, generally more so in fasted than in unrestricted fed lambs.
Oddy
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VH
Elizabeth Macarthur Agricultural Institute, New South Wales Agriculture, Camden, Australia.
Owens
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PC
D000818:Animals; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007261:Infusions, Intra-Arterial; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption; D011506:Proteins / Q000378:metabolism*; D012756:Sheep
D011506:Proteins; D007334:Insulin-Like Growth Factor I; D005947:Glucose; D010100:Oxygen