Lactate kinetics in exercising Thoroughbred horses: regulation of turnover rate in plasma.

The research is about how plasma lactate turnover rate in Thoroughbred racehorses changes with exercise and how such changes are regulated. The study also explores the role of lactate as a metabolic fuel in trained animals.

Goals and Methods

• The study pursued two main objectives: to understand the effect of changes in cardiac output and plasma lactate concentration on turnover rate, and to gauge the importance of lactate as a metabolic fuel in a trained athlete animal.
• The researchers used bolus injection of [U-14C]lactate to measure the plasma lactate turnover rate in Thoroughbred racehorses at rest and during two levels of submaximal treadmill exercise (a trot at 3-4 m/s with a 6% incline, and a horizontal canter at 6.5 m/s).

Results and Observations

• The lactate turnover rates were calculated to be 9.3 mumol.min-1.kg-1 at rest, 75.9 mumol.min-1.kg-1 at the beginning of the trot protocol (at 45% maximum O2 uptake, VO2max), 50.3 mumol.min-1.kg-1 later in the same trot protocol (at 50% VO2max), and 66.1 mumol.min-1.kg-1 during the canter protocol (at 55% VO2max).
• Substantial changes in both cardiac output and plasma lactate concentration were seen to have significant effects on turnover rate.
• The research indicates that in Thoroughbreds, variations in plasma lactate fluxes during exercise follow standard mammalian patterns. However, lactate plays only a minor role as an oxidizable fuel in horses, accounting for less than 5% of metabolic rate (VO2) during submaximal work.

Conclusion

• The study concludes that the adjustments in cardiac output and metabolite concentration represent the coarse and fine controls, respectively, for regulating the turnover rate of plasma metabolites in Thoroughbred horses.