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Isolation-Perfusion of Ovine Hind Limbs II. Amino Acid Metabolism¹

University of Kentucky³, Lexington 40506

Abstract

The hind limbs from seven ovine wethers were isolated and tissue viability maintained via isolation-perfusion utilizing an artificial heart-lung apparatus. Perfusate samples were taken at 30-min. intervals during a 2-hr, perfusion period. There was a linear decrease in plasma concentration of total essential amino acids and a linear increase in total nonessential amino acids during the 2-hr, perfusion period. Although there was an increase or decrease of several of the amino acids during perfusion, the magnitude of change was relatively small. There was a trend toward an increase in total amino acid concentration by the end of the perfusion period. Also, after 2-hr, of perfusion, the plasma concentration of most amino acids was near the levels observed in plasma of fasted wethers. A radioactive isotope of leucine (¹⁴C-L-leucine) was included in the perfusate. Data from the isotope study suggest a dynamic exchange of amino acids between a cellular pool, or pools, and the plasma pool. The half-time estimate for uptake of total radioactivity (¹⁴C-L-leucine) was 55.3 ± 5.3 minutes. These data suggest that the muscle tissue in isolated-perfused ovine hind limbs is relatively sensitive to plasma amino acid levels and tends to maintain a balance of amino acids at a rather constant level, especially when the plasma pool approximates levels of wethers in a fasted condition. The participation of muscle tissue in maintaining plasma amino acid homeostasis would tend to help explain why plasma free amino acid concentrations of peripheral blood are not always sensitive indicators of the nitrogen status of intact ruminants.

¹ The investigation reported in this paper (73-5-168) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director.

² Present address: Clemson University, Clemson, South Carolina 29631

³ Department of Animal Sciences.