Single-injection glucose kinetics with compartmental modelling during rest and low-intensity exercise in horses

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

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.

Twelve exercise trained Arabian geldings received a bolus of 100 µmol/kg bwt [6,6-(2) H]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.

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).

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

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