Does the type of exercise affect tryptophan catabolism in horses?

The Influence of Exercise Intensity on Tryptophan Metabolites in Thoroughbred Horses

“…Thus, once again, we believe that the transient increase in Kyn of only 26% resulting from the high-intense exercise reported in the current study is unlikely to cause mental problems. Plasma 3-HKyn concentration did not show significantly important differences in response to exercise such as in Arabian horses studied previously [ 12 ]. However, an insignificant increase in 3-HKyn levels observed 60 min after the end of the intense exercise correlated positively with the exercise-induced increase in LA values.…”

“…This means that a transient drop in Trp is unlikely to have any negative consequences, especially since the NAm concentration in blood increases and potentially facilitates substrate for NAD + synthesis entering the NAD + salvage pathway synthesis [ 2 ]. The exercise-induced decrease in Trp was also reported in purebred Arabian horses in response to an endurance effort without a detectable influence on horse mood and behavior [ 12 , 20 ]. The stated increase in Kyn was also transient and did not correlate with the increase in LA.…”

“…The stated increase in Kyn was also transient and did not correlate with the increase in LA. Similarly, the increase in plasma Kyn concentration was noted 30 min after short-time intense exercise in purebred Arabian horses [ 12 ]. Kyn is a potentially depression-inducing agent; however, doses ten time higher than physiological levels are known to induce depressive-like behavior in experimental animals [ 21 ].…”

“…Both mentioned Trp catabolism pathways are modulated by physical activity [ 6 , 7 ]. In athletic horses, significant increases in plasma Trp, 5-HT, Kyn, Kyna and XA in response to different types of exercise were reported [ 8 , 9 , 10 , 11 , 12 ]. The changes in Trp levels were studied also in other horses and showed no important change during trot on the treadmill with increasing speed or cantering lasting 15 min, defined by the authors as medium-heavy exercise [ 13 , 14 ], whereas jumping (the standardized obstacle course) or endurance, low-intense exercise led to a decrease in plasma Trp concentration [ 12 , 15 ].…”

“…The changes in Trp levels were studied also in other horses and showed no important change during trot on the treadmill with increasing speed or cantering lasting 15 min, defined by the authors as medium-heavy exercise [ 13 , 14 ], whereas jumping (the standardized obstacle course) or endurance, low-intense exercise led to a decrease in plasma Trp concentration [ 12 , 15 ]. Additionally, our group has earlier reported that an endurance exercise leads to a decrease in the plasma level of NAm [ 12 ]. Thus, probably, the intensity of exercise performed by the horse is the main factor regulating the Trp metabolism.…”