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Glutamate and glutamine metabolism in tissues of developing lambs
- Jennifer M. Pell, Julia Tooley, Marjorie K. Jeacock, D. A. L. Shepherd
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- Journal:
- The Journal of Agricultural Science / Volume 101 / Issue 2 / October 1983
- Published online by Cambridge University Press:
- 27 March 2009, pp. 265-273
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The activities of glutamine synthetase, phosphate-dependent glutaminase, phosphate-independent glutaminase, glutamate dehydrogenase, γ-glutamyl transferase and glutamine-oxo-acid aminotransferase were assayed in liver, kidney cortex, brain (cerebral hemispheres), spleen, skeletal muscle and ileum obtained from lambs of 100–260 days conceptual age. A curve was fitted to each set of data relating enzyme activity and conceptual age.
In the ileum, glutaminase and γ-glutamyl transferase activities declined during development. Glutamine synthetase activity in the spleen increased markedly after birth, whereas glutamate dehydrogenase activity declined as rumen function was established. In the liver, glutamate dehydrogenase and glutamine synthetase activities were highest in suckling lambs and there was a gradual increase in hepatic γ-glutamyl transferase activity throughout the period studied. The activity of phosphate-dependent glutaminase was lowest in the kidney cortex of ruminating lambs but renal activities of glutamate dehydrogenase, phosphate-independent glutaminase, glutamine synthetase and γ-glutamyl transferase were highest in ruminating lambs. In skeletal muscle, a gradual increase in glutamine synthetase activity occurred after 180 days conceptual age, whereas there was no detectable glutaminase activity in ruminating lambs. In the brain, there was an increase in glutamate dehydrogenase, phosphatedependent glutaminase and glutamine synthetase activities during the foetal and early suckling periods, whereas γ-glutamyl transferase activity increased throughout the period studied.
Glutamine-oxo-acid aminotransferase activity was not detected in any of the tissues studied. Phosphate-independent glutaminase activity was always less than 10% of phosphate-dependent glutaminase activity and therefore must have a minor role in the metabolism of glutamine in lambs.
A consideration of the relative activities of the enzymes at different stages of development indicated that the ileum, spleen, liver, kidney cortex and brain have a substantial potential for glutamine utilization during foetal life. As a lamb matures after birth, there are changes in the metabolism of glutamate and glutamine which indicate that there is a greater potential for net glutamine synthesis in older lambs. This could be associated with the need for detoxification of ammonia in ruminating lambs.
Glutamate and glutamine metabolism in the ovine placenta
- Jennifer M. Pell, Marjorie K. Jeacock, D. A. L. Shepherd
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- Journal:
- The Journal of Agricultural Science / Volume 101 / Issue 2 / October 1983
- Published online by Cambridge University Press:
- 27 March 2009, pp. 275-281
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The concentration of glutamate and of glutamine was measured in whole blood obtained from a maternal artery, a uterine vein, a foetal artery and an umbilical vein of chronically catherized ewes and foetuses from 100 to 140 days after conception. The activities of glutamate dehydrogenase, phosphate-dependent glutaminase, phosphateindependent glutaminase, glutamine synthetase, γ-glutamyl transferase and glutamine-oxo-acid aminotransferase were measured in placentomes obtained from ewes during a similar period of gestation.
The concentrations of glutamate in blood from maternal vessels remained constant, whereas there was a significant decline (P < 0·001) in the concentration of glutamate in foetal blood. Glutamine concentrations declined significantly (P < 0·05) in maternal blood and in foetal arterial blood (P < 0·001), whereas the concentration of glutamine in umbilical venous blood remained constant.
Mean arterio-venous differences for glutamate indicated that there was no net uptake from or release into maternal blood by the uterus. However, there was a significant (P < 0·02) uptake of glutamate by the placenta from the foetal circulation. Glutamine release from the placenta into the foetal circulation increased as the foetus matured.
Significant activities of glutamate dehydrogenase, γ-glutamyl transferase, glutamine synthetase and phosphate-dependent glutaminase were found in the placenta but there was no significant relationship between the activities of these enzymes and the gestational age of the foetus. The enzyme profile indicated that the placenta has a substantial potential for net glutamine synthesis.
It is concluded that, for a 140-day foetus, the release of glutamine from the placenta accounts for more than half of its nitrogen requirement. Direct placental transfer of glutamine from maternal blood accounts for only one-third of the glutamine released by the placenta into the foetal circulation of a 140-day foetus. Therefore, the remainder of the glutamine is synthesized in the placenta from glutamate. Only one-third of the glutamate required for this placental glutamine synthesis is from the glutamate released by the foetus. The remainder must be derived either from 2-oxoglutarate, as the result of aminotransferase or glutamate dehydrogenase activities, or from glutathione by the action of γ-glutamyl transferase.
The interaction between nutritional status and growth hormone in young cattle: differential responsiveness of fat and protein metabolism
- Janet M. Dawson, Henry M. R. Greathead, Jim Craigon, David L. Hachey, Peter J. Reeds, Jennifer M. Pell, Peter J. Buttery
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- Journal:
- British Journal of Nutrition / Volume 79 / Issue 3 / March 1998
- Published online by Cambridge University Press:
- 09 March 2007, pp. 275-286
- Print publication:
- March 1998
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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 × maintenance energy requirement, offered in hourly portions. Continuous intravenous infusions of [1-13C]leucine or [1-13C]palmi-tate 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.