Evaluation of glutamine, ammonia and cortisol in endurance horses during races of different lengths

Abstract

Glutamine is the most abundant free amino acid in the bodies of mammals. It is very important for cell proliferation, metabolism of ammonia and energy production in skeletal muscles, especially during aerobic exercise. The aim of this study was to investigate if serum levels of glutamine and ammonia could be models for studying the dynamics of this important amino acid during exercise in endurance horses, as these animals are subjected to prolonged and intense aerobic workloads. Thirty-three endurance horses that competed in the categories of 80 km (n = 13), 120 km (n = 14) and 160 km (n = 5) in four races were tested. There was no statistical difference in the levels of glutamine between moments (P > 0.05), but there was a significant increase in plasma levels of ammonia right after the race (P < 0.05). This increase is more marked in the horses that ran 80 km, followed by those that ran 120 km and finally by those running 160 km. There was a positive correlation between the levels of ammonia and glutamine in categories 160, 120 and 80 km (r = 0.209, r = 0.151 and r = 0.176, respectively; P < 0.05). Oscillations in serum levels of glutamine are difficult to detect in endurance horses, since oxidative muscle fibers are important reservoirs of this amino acid. Also, it is difficult to know about glutamine consumption because of the organic reserves and ease of metabolization; hence, measuring ammonia as an indicator of consumption of glutamine. We concluded that ammonia and cortisol levels can serve as indirect measures of the use of glutamine during aerobic exercise and both can be markers of effort.