Dehydration, electrolyte imbalances and renin-angiotensin-aldosterone-vasopressin axis in successful and unsuccessful endurance horses

P>Reason for performing study: Limited information exists concerning the defence of homeostasis during endurance competitions and the relationship with performance. Objectives: This research analysed renin (REN), angiotensin II (ANG), aldosterone (ALD) and vasopressin (AVP) in horses covering different distances, assesses differences between successful and eliminated horses and evaluates correlations between hydration status, renal function, electrolytes, REN, ANG, ALD and AVP. Methods: Packed cell volume (PCV), velocity and serum concentrations of REN, ANG, ALD, AVP, Na, K, Cl, Ca, Mg, P, creatine kinase, aspartate aminotransferase, lactate dehydrogenase, total proteins (TSP), albumin (ALB), serum ureic nitrogen (SUN), creatinine (CREAT) and lactate were analysed in both successful horses (SH) and in horses eliminated due to metabolic problems (MH). Two types of competition were studied: 91 km in one day (Competition A: 20 SH, 9 MH) and 166 km in 2 days, 83 km/day (Competition B: 10 SH and 5 MH). Results: Research analysed renin was not affected by exercise, whereas ANG, ALD and AVP increased. In the SH group, resting ALD and AVP concentrations at the beginning of the second day of Competition B were higher than preride values. Vasopressin did not change during the second day of Competition B, whereas ALD progressively increased. Metabolic problems of both groups showed more evident dehydration (higher PCV, TSP, ALB, SUN and CREAT) and electrolyte alterations (more intense decreases of Na and Cl) than SH at the different sampling times. Metabolic problems presented higher ALD and AVP concentrations. Angiotensin II was higher at certain sampling times in the horses. Conclusions: Endurance horses with dehydration and electrolyte disturbances showed a more intense activation of the REN-ANG-ALD-AVP axis. Potential relevance: The study of the response of the REN-ANG-ALD-AVP axis during prolonged exercise in horses with different performance will aid to minimise the risk of metabolic diseases during competitions.