New scenarios in the way in which metabolic adaptations are viewed in Endurance horses have been raised by scientists in Italy.
Katia Cappelli and her fellow researchers described Endurance as one of the most challenging equestrian disciplines. Endurance horses are susceptible to metabolic imbalance through dehydration, acid balance and electrolyte abnormalities. There is also the risk of heat accumulation, which can trigger life-threatening conditions.
Endurance horses are subjected to specific training that induces the adaptations required for prolonged moderate-intensity exercise on different ground surfaces and under different weather conditions. The training is dominated by aerobic conditioning.
The University of Perugia researchers, writing in the journal Genes, said evidence has been found that alterations in circulating micro RNA expression are triggered by physical exercise and endurance. These micro-RNAs include regulatory molecules that play active roles in cell differentiation, proliferation and metabolism.
The researchers in Italy set out to gain a deeper molecular knowledge of responses to prolonged moderate-intensity exercise in endurance horses, and to identify circulating micro RNA molecules related to non-physiological responses.
Their hypothesis was that differences in circulating micro RNA in horses after race elimination could provide clues to a reduced adaptation to exercise stress, leading to low-performance syndromes and diseases.
They measured serum micro RNA profiles in 18 horses taking part in national and international endurance competitions. Profiles from eight of the horses, eliminated because of metabolic imbalances, were compared to those of 10 horses who finished their endurance competitions in excellent metabolic condition.
Differences were identified by the study team.
In the better-performing horses, they found up-regulation of a set of micro RNAs involved in several key processes that included cardiac and skeletal muscle remodeling, the formation of new blood vessels, ventricular contractility, and in the regulation of gene expression.
“Our preliminary data open new scenarios in the definition of metabolic adaptations to the establishment of efficient training programs and the validation of athletes’ elimination from competitions,” they said.
The horses who failed to finish showed signs of severe dehydration in their blood and biochemical profiles. They had higher values of hematocrit, hemoglobin, creatinine, total plasma proteins, albumins, and increased protein catabolism indicated by higher serum urea concentration.
High levels of muscle enzyme markers were found, as expected, in the serum of both groups, but there were no significant differences observed among the finishers and non-finishers in terms of enzymes.
“This confirmed the low correlation between these serum enzyme levels and the poor performance of equine athletes as suggested by other authors.”
This indicates that deeper knowledge is needed about molecular events affecting the response to physical stress that can also lead to metabolic alterations and low performance.
Micro RNAs are ideal molecules for this purpose because of their properties and their fast response to physiological stress, the researchers said.
The study results show that, besides skeletal muscle, other tissues may be involved in a horse’s adaptation to exercise-induced stress, since physiological stress induced by exercise triggers multi-organ responses in skeletal muscle, blood vessels, the heart and lungs.
“As a whole, the results seem to indicate that the non-performing horses failed to adapt to exercise-induced stress,” they said.
In conclusion, for the non-performing horses, the results suggest a specific circulating micro RNA profile pointing towards molecular mechanisms and metabolic pathways underlying the inability of tissues and organs to adapt to stress induced by prolonged physical exercise and training.
Modulation of skeletal muscle tissue development, cardiac and skeletal muscle remodeling, blood vessel formation, ventricular contractility and the regulation of gene expression appear to be the most involved processes.
They said their work amounted to a preliminary investigation. Validation with alternative techniques and a larger number of horses, and possibly time-course sampling, will be valuable in this intriguing field of research.
The study team comprised Cappelli, Samanta Mecocci, Stefano Capomaccio, Francesca Beccati, Andrea Rosario Palumbo, Alessia Tognoloni, Marco Pepe and Elisabetta Chiaradia.
Cappelli, K.; Mecocci, S.; Capomaccio, S.; Beccati, F.; Palumbo, A.R.; Tognoloni, A.; Pepe, M.; Chiaradia, E. Circulating Transcriptional Profile Modulation in Response to Metabolic Unbalance Due to Long-Term Exercise in Equine Athletes: A Pilot Study. Genes 2021, 12, 1965. https://doi.org/10.3390/genes12121965