Plasma glutamine status in the equine at rest, during exercise and following viral challenge

The variation over 24 h of plasma glutamine concentration in nonexercising horses was studied in 3 Thoroughbreds (TB) fed at 1600 h and 0700 h. This indicated a small but regular change associated with feeding. Starting at a mean of 482 mumol/l at 1600 h the concentration increased to 522 mumol/l at 2000 h, falling to 476 mumol/l at 1600 h and increasing again to 525 mumol/l at 2000 h. 'Normal' values were established in 19 part-bred TB horses, lacking clinical signs or remarkable pathology and in light training, by sampling weekly at 1000 h over a 10 week period. The mean concentration was 491 mumol/l. Values were normally distributed with 95% confidence range between horses of 469-512 mumol/l. The s.d. of values within-horse was 28 mumol/l. The acute effect of exercise was investigated in 5 TB horses during i) an exercise simulating the road and tracks phase of a 3-day-event and ii) a sustained high-intensity exercise test (115% VO2max until the pace was no longer maintained). In both tests a transient increase was produced as a direct result of exercise, followed by a decline to a nadir at approximately 3 h post exercise. Pre-exercise resting concentrations, following either test, were approaching pre-values by 24 h recovery. The effect of viral challenge was studied in 6 TB horses exposed to an aerosol of equine influenza virus, subtype H3N8 (A/equine-2 subtype) which caused mild clinical signs. A significant fall in the 1000 h plasma glutamine concentration from a mean of 463 to 342 mumol/l by the 6th day was seen in 5 horses. A more gradual decline was observed in the 6th horse. These findings indicate a similar response to viral challenge in the horse to that in man.