The interaction between nutritional status and growth hormone in young cattle: differential responsiveness of fat and protein metabolism.
The effect of dietary intake level on in vivo plasma leucine and plasma palmitate flux rates and on the response to a bolus injection of bovine growth hormone (GH) was investigated in six young steers. Animals were fed on a pelleted diet of dried grass-barley (0.7:0.3, w/w) in quantities sufficient to supply 0.8, 1.2, 1.6, 2.0, 2.4 or 2.65 x maintenance energy requirement, offered in hourly portions. Continuous intravenous infusions of [1-13C]leucine or [1-13C]palmitate were used to determine the flux of amino acid and fatty acid through the plasma pool before, immediately (1-3 h) after and 22-24 h after a subcutaneous injection of bovine GH (0.55 mg/kg body weight). Hourly blood samples were taken for 27 h to monitor the temporal responses of circulating hormones and metabolites following GH administration. The animal on the lowest plane of nutrition had elevated plasma GH and reduced insulin-like growth factor-1 concentrations compared with those fed on higher intake levels. Plasma leucine flux and leucine concentration increased with intake while palmitate flux and plasma non-esterified fatty acid (NEFA) concentrations were inversely related to intake. Leucine flux rate decreased in the animals fed on the two highest intake levels in response to GH 22-24 h after administration, but plasma leucine concentrations were reduced in all animals at this time. Only the animal fed on the lowest intake level showed an immediate response to GH (within 3 h of administration) with increased palmitate flux and plasma NEFA concentrations but a lipolytic response was apparent in other animals 22-24 h post-administration although the magnitude of the response was markedly reduced at high intakes. We conclude that lipid and protein metabolism are differentially responsive to GH and nutritional status.
Dawson
J M
JM
School of Biology, University of Nottingham, Loughborough, UK. Janet.Dawson@nottingham.ac.uk
Greathead
H M
HM
Craigon
J
J
Hachey
D L
DL
Reeds
P J
PJ
Pell
J M
JM
Buttery
P J
PJ
D000818:Animals; D002247:Carbon Isotopes; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007930:Leucine / Q000378:metabolism / Q000494:pharmacology; D050356:Lipid Metabolism; D008297:Male; D009752:Nutritional Status; D010168:Palmitates / Q000378:metabolism / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology
D002247:Carbon Isotopes; D005230:Fatty Acids, Nonesterified; D010168:Palmitates; D011506:Proteins; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D007930:Leucine