Muscle glycogen breakdown and lactate metabolism during intensive exercise in Thoroughbred horses

Abstract

We examined the muscle glycogen, and muscle and plasma lactate concentrations before and after 1 and 2 min of intensive exercise at 120% V ・ O 2 max, and examined possible relationships between these indexes and protein levels of monocarboxylate transporters (MCT) in the gluteus medius muscle of Thoroughbred horses. The horses underwent 1 and 2 min of intensive exercise at the speed of 120% maximal oxygen consumption (V ・ O 2 max) on a treadmill. The plasma lactate concentration increased after 1-min exercise (11.7 ± 0.8 mmol/L) and 2-min exercise (23.1 ± 1.1 mmol/L). The muscle lactate concentration increased after 1-min exercise (17.3 ± 2.1 mmol/kg) and 2-min exercise (23.6 ± 2.0 mmol/kg). While there was no significant difference in lactate accumulation in the plasma between the first minute and the second minute, lactate accumulation in muscle significantly decreased in the second minute compared with the first minute. The muscle glycogen level decreased after both 1-(42%) and 2-min (41%) exercise, but there was no difference between the levels after 1-and 2-min exercise. The muscle lactate concentration after 2-min intensive exercise positively correlated with the protein level of MCT4 (r = 0.78, p < 0.01). These results suggest that glycogen breakdown occurs in the first minute of intensive exercise, and Thoroughbred horses with higher muscle lactate production during exercise are endowed with higher expression of MCT4, that facilitates the efflux of lactate from muscle cells.

Metabolic and Biomolecular Changes Induced by Incremental Long-Term Training in Young Thoroughbred Racehorses during First Workout Season

“…In our study, the highest values at rest were identified at T60, probably due to the beginning of the maximal sprint exercise levels. Often, lactate has been argued to be a molecule mainly responsible of fatigue, but new data suggest this molecule may be an efficient energy source and plays an important role in exercise-mediated adaptation [30]. Thoroughbred horses have a higher capacity to sustain maximal exercise than other breeds, and it is attributable to their physiological characteristics, such as a high maximal oxygen uptake (VO 2 max), large stores of muscle glycogen, and high glycolytic and oxidative capacity, thus resulting in a high capacity for lactate production and oxidation [29,30].…”

Lactate as a Signaling Molecule That Regulates Exercise-Induced Adaptations

“…From this perspective, lactate production (in glycolytic fibers) and reduction into pyruvate (oxidative fibers) change the cell redox balance, a process that has particular importance during high-intensity exercise [12]. It should also be noted that lactate aerobic metabolism has been suggested to be an important energy source during high-intensity exercise [13,14]; thus, this process is of relevance during that exercise modality. <<=LDHBPyruvate + NADH + + H + ⟸======⟹ Lactate + NADLDHA=>>…”

011 The Effect of Various Levels of Dietary Starch on Glycogen Replenishment in the Light Working Horse

“…The gallops resulted in similar glycogen depletion, amounting to approximately 19 % to 25 % of resting concentration. Skeletal muscle glycogen concentration returned to resting values by 72 h. Kitaoka et al (2014) found that 1 or 2 min of intensive exercise on an inclined (6.0º) treadmill at 120 % VO2max (maximal oxygen uptake) also significantly depletes glycogen. The greater levels of depletion in this study may be due to the use of a treadmill and uphill running (Valberg, 1986;Kitaoka et al, 2014).…”

“…Skeletal muscle glycogen concentration returned to resting values by 72 h. Kitaoka et al (2014) found that 1 or 2 min of intensive exercise on an inclined (6.0º) treadmill at 120 % VO2max (maximal oxygen uptake) also significantly depletes glycogen. The greater levels of depletion in this study may be due to the use of a treadmill and uphill running (Valberg, 1986;Kitaoka et al, 2014). Davie et al (1999) there was no significant difference between skeletal muscle glycogen concentration before the protocols, there was a significant decrease in concentration in protocols A and B in relation to the control group after the protocols were performed.…”