The influence of metabolic alkalosis upon exercise metabolism in the thoroughbred horse.

Six thoroughbred horses exercised on a motorised treadmill on two separate occasions at a speed of 11 or 12 m.s-1 for up to 2 min. 4 h prior to exercise each horse was given a 21 test solution of sodium bicarbonate (NaHCO3; 0.6 g.kg-1 body mass) or a control solution of water by nasogastric intubation, the order of administration of the two solutions was randomised. Blood samples (n = 15) were obtained before and during the 4 h after intubation, during exercise and for 30 min after exercise. NaHCO3 ingestion resulted in changes in pre-exercise acid-base status. The changes in blood lactate and base excess with exercise were greater after NaHCO3 administration; after 1 min of exercise in the case of lactate (P less than 0.05) and immediately after exercise in the case of base excess (P less than 0.05). Plasma ammonia levels were lower during (P less than 0.05) and immediately after (P less than 0.05) exercise following NaHCO3 ingestion. The peak change in plasma ammonia with exercise was also lower after NaHCO3 ingestion (P less than 0.05). Following exercise after NaHCO3 ingestion, five horses demonstrated lower muscle adenosine 5-triphosphate loss (P less than 0.05) and inosine 5-monophosphate formation (P = 0.05) and higher glycerol 3-phosphate formation (P less than 0.05). There is evidence to suggest that metabolic alkalosis may delay the onset of fatigue by decreasing the extent of adenine nucleotide loss during high-intensity exercise.