Epinephrine inhibits exogenous glucose utilization in exercising horses

Area of Science:

• Equine physiology
• Exercise metabolism
• Carbohydrate biochemistry

Background:

• Understanding carbohydrate metabolism is crucial for equine athletic performance.
• Preexercise nutrition strategies can impact energy availability during exercise.
• The role of glucose and epinephrine in modulating fuel use in horses requires further elucidation.

Purpose of the Study:

• To investigate the impact of preexercise oral glucose administration on carbohydrate metabolism in horses during moderate-intensity exercise.
• To determine the influence of concurrent epinephrine infusion on these metabolic responses.
• To compare fuel utilization patterns under different preexercise conditions.

Main Methods:

• Six horses underwent 60 minutes of treadmill exercise at 55% maximum oxygen uptake.
• Three trials were conducted: oral glucose (G), oral glucose with epinephrine infusion (GE), and water control (F).
• Plasma glucose, insulin, and epinephrine concentrations, glucose kinetics, and muscle glycogen utilization were measured.

Main Results:

• Oral glucose administration led to hyperglycemia and hyperinsulinemia in both G and GE trials.
• Glucose rate of appearance increased with glucose administration, but epinephrine infusion blunted the glucose rate of disappearance.
• Muscle glycogen utilization was significantly higher in the GE trial compared to F and G trials.

Conclusions:

• Preexercise glucose enhances plasma glucose utilization during exercise in horses without affecting muscle glycogen use.
• Epinephrine infusion inhibits the glucose uptake response to preexercise glucose administration.
• Epinephrine increases the reliance on muscle glycogen as an energy source during exercise when glucose is administered.