Route of carbohydrate administration affects early post exercise muscle glycogen storage in horses.
BACKGROUND
No studies in horses have examined the effect of route of carbohydrate (glucose) administration on the rate of muscle glycogen storage following glycogen-depleting exercise.


OBJECTIVE
Glucose delivery from the gastrointestinal tract limits the rate of muscle glycogen storage following glycogen-depleting exercise.


METHODS
In a crossover design, 7 fit horses completed treadmill exercise (EX) on 3 occasions to deplete muscle glycogen by approximately 50%. After EX horses received: 1) i.v. glucose infusion (IV; 0.5 g/kg bwt/h for 6 h), 2) oral glucose boluses (OR; 1 g/kg bwt at 0, 2 and 4 h post EX) or 3) no glucose supplementation (CON). Blood samples for measurement of glucose and insulin concentrations were collected before EX and during the 6 h treatment period. Muscle biopsies for measurement of muscle glycogen content (GLY) and glycogen synthase (GS) activity were taken before and after exercise and at 3 and 6 h.


RESULTS
Mean plasma glucose concentrations were significantly higher in IV and OR than in CON throughout treatment. The average serum insulin responses in IV and OR treatments were also significantly greater than in CON. After EX, GLY was not different among the 3 treatments. However, glycogen storage rates were significantly higher in IV than in CON and OR during the first 3 h and second 3 h of recovery, and GLY was significantly higher in IV than in OR and CON at 6 h of recovery. GS activity was significantly higher in IV than in OR and CON at 3 h of recovery.


CONCLUSIONS
Muscle glycogen storage in horses during a 6 h period after exercise was enhanced by i.v. glucose administration (3 g/kg) but not by an equivalent glucose dose administered per os. While oral administration of glucose achieved a level of hyperglycaemia and hyperinsulinaemia that markedly accelerates glycogen storage in other species, the rate of glycogen storage following oral supplementation was not different to control conditions.


CONCLUSIONS
Glucose supplementation via the i.v. route should be considered when rapid replenishment of muscle glycogen stores is desired.
Geor
R J
RJ
Department of Biomedical Science, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
Larsen
L
L
Waterfall
H L
HL
Stewart-Hunt
L
L
McCutcheon
L J
LJ
D000284:Administration, Oral; D000818:Animals; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000008:administration & dosage* / Q000378:metabolism / Q000493:pharmacokinetics*; D005260:Female; D006003:Glycogen / Q000096:biosynthesis*; D006006:Glycogen Synthase / Q000378:metabolism; D006736:Horses / Q000378:metabolism* / Q000502:physiology; D007262:Infusions, Intravenous / Q000662:veterinary; D007328:Insulin / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D010805:Physical Conditioning, Animal / Q000502:physiology*
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D007328:Insulin; D006003:Glycogen; D006006:Glycogen Synthase