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Keywords:

  • horse;
  • glucose kinetics;
  • endurance exercise;
  • compartmental model;
  • single injection tracer;
  • metabolism

Summary

Reasons for performing study: Tools and criteria to evaluate and understand glucose metabolism are essential to optimise equine energy utilisation for exercise performance and reduced metabolic health risks.

Objectives: To re-evaluate models of glucose kinetics in the horse at rest and during endurance type exercise using a single injection technique and compartmental modelling.

Methods: Twelve exercise trained Arabian geldings received a bolus of 100 µmol/kg bwt [6,6-2H]glucose i.v. while at rest and while running at ∼4 m/s on a treadmill. Tracer and tracee glucose curves from 4–150 min after the bolus dose (while the subject maintained its resting or exercising state) were described by a 2 term exponential decay curve. Compartmental modelling was performed simultaneously for each horse's resting and exercise curves using an ‘exercise effect’ parameter for each compartmental exchange rate during exercise.

Results: Exercise increased all rate constants and transport flows for glucose between compartments by 110–145% (P≤0.004). Total glucose transport through the system increased from 8.9 ± 0.6 µmol/min/kg/bwt at rest to 25.0 ± 1.1 µmol/min/kg bwt during exercise (P<0.001). Exercise decreased the volume of the primary glucose compartment by 8% (P = 0.006) and increased plasma glucose clearance rate by almost 200% (P<0.001). Turnover times and mean residence times were decreased approximately 60% by exercise (P<0.001), whilst turnover rates were increased 125% (P<0.001).

Conclusions: Single-injection tracer kinetics and compartmental modelling represent a valuable tool to quantify tracee availability to and use by tissue.

Potential relevance: This technique could represent a beneficial tool for future studies exploring the role of glucose metabolism in equine exercise performance and metabolic disease.