Effect of amino acid and glucose administration following exercise on the turnover of muscle protein in the hindlimb femoral region of thoroughbreds.

Reasons For Performing Study: In man, muscle protein synthesis is accelerated by administering amino acids (AA) and glucose (Glu), because increased availability of amino acids and increased insulin secretion, is known to have a protein anabolic effect. However, in the horse, the effect on muscle hypertrophy of such nutrition management following exercise is unknown.

Objectives: To determine the effect of AA and Glu administration following exercise on muscle protein turnover in horses. We hypothesise that administration of AA and Glu after exercise effects muscle hypertrophy in horses, as already shown in man and other animals.

Methods: Measurements of the rate of synthesis (Rs) and rate of degradation (Rd) of muscle protein in the hindlimb femoral region of thoroughbred horses were conducted using the isotope dilution method to assess the differences between the artery and iliac vein. Six adult Thoroughbreds received a continuous infusion of L-[ring-2H5]- phenylalanine during the study, the stable period for plasma isotope concentrations (60 min), resting periods (60 min), treadmill exercise (15 min) and recovery period (240 min). All horses were given 4 solutions (saline [Cont], 10% AA [10-AA], 10% Glu [10-Glu] and a mixture with 10% AA and 10% Glu [10-Mix]) over 120 min after exercise, and the Rs and Rd of muscle protein in the hindlimb measured.

Results: The average Rs during the 75-120 min following administration of 10-Mix was significantly greater than for the other solutions (P<0.05). The second most effective solution was 10-AA, and there was no change in Rs after 10-Glu.

Conclusions: Administration of AA following exercise accelerated Rs in the hindlimb femoral region, and this effect was enhanced when combined with glucose, because of increasing insulin secretion or a decreased requirement for AA for energy.

Potential Relevance: Further studies are required regarding the effect on muscle hypertrophy of supplementing amino acids and glucose in the feed of exercising horses.