Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers.
Insulin-like growth factor-1 (IGF-1) is perhaps the most important endogenous factor controlling growth. Most studies to date in livestock have shown that IGF-1 has greatest efficacy when animals are in a catabolic state. We have determined the effects of an i.v. infusion of the IGF-1 analog Long(R3)-IGF-1 on protein metabolism in beef heifers that were slowly losing liveweight because of restricted feeding. There was a tendency for both whole-body protein and skeletal muscle protein to be conserved in Long(R3)-IGF-1-treated heifers. Long(R3)-IGF-1 administration markedly reduced the plasma concentrations of all amino acids measured and glucose. There was a significant change in the profile differences of endogenous plasma IGF-1 concentrations during the 8-hr infusion period, with plasma IGF-1 decreasing sharply in the test group. There was a significant difference in mean profiles for plasma IGF-2 between the test and control groups. Overall, plasma IGF-2 for the control group decreased only slightly over time (about 40 ng/ml), whereas the test group decreased dramatically (by about 140 ng/ml). Increased plasma concentrations of a 31-32-kDa IGF-binding protein (possibly IGF-binding protein-1) in the treated group was detected by radioligand blot. We found that Long(R3)-IGF-1 infusion tended to preserve whole-body and muscle protein in beef heifers on a low-quality diet, and suggest that further investigation of this treatment may provide an alternative approach to reducing weight loss during the dry season.
Hill
R A
RA
Queensland Beef Industry Institute, Department of Primary Industries, Australia. HillR@dpi.gld.gov.au
Hunter
R A
RA
Lindsay
D B
DB
Owens
P C
PC
D000596:Amino Acids / Q000097:blood; D000818:Animals; D001315:Australia; D001786:Blood Glucose / Q000032:analysis; D015153:Blotting, Western / Q000662:veterinary; D002417:Cattle / Q000254:growth & development*; D002851:Chromatography, High Pressure Liquid / Q000662:veterinary; D005260:Female; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000031:analogs & derivatives* / Q000502:physiology; D011506:Proteins / Q000378:metabolism*; D014508:Urea / Q000097:blood; D015431:Weight Loss
D000596:Amino Acids; D001786:Blood Glucose; D018970:Insulin-Like Growth Factor Binding Protein 1; D011506:Proteins; D007334:Insulin-Like Growth Factor I; D014508:Urea