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Changes in plasma atrial natriuretic peptide concentration in exercising horses in relation to hydration status and
S Nyman1, U M Kokkonen, K Dahlborn
1Department of Medicine and Surgery, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala.
Objective:
To investigate effects of hydration status and exercise intensity on plasma atrial natriuretic peptide (ANP) concentration in exercising horses.
Animals:
4 trained Standardbreds.
Procedure:
Horses performed a 40-minute exercise test at 65 to 70% maximal heart rate (HRmax; no incline) and a 12-minute test at approximately 90% HRmax (3.5 degrees incline). The 40-minute test was performed with ad libitum access to drinking water (normohydration), after water had been withheld for 24 hours (dehydration), and 30 minutes after 12 L of water at body temperature had been given via nasogastric tube (hyperhydration). The 12-minute test was only performed with normohydrated horses.
Results:
Plasma ANP concentration was higher toward the end of exercise during hyperhydration than during the other 2 hydration states, and the area under the plasma ANP concentration curve was significantly greater during hyperhydration than during dehydration. The maximal plasma ANP value induced during the 12-minute test was similar to that of the 40-minute test. After the 12-minute test, plasma ANP concentration did not decrease during the first 30 minutes of recovery, whereas after the 40-minute test, plasma ANP concentration decreased by approximately 30% during the same period.
Conclusions:
Hydration status can affect plasma ANP concentration in horses during submaximal exercise. Maximal plasma ANP concentration was similar at the 2 exercise intensities studied, but the postexercise return to baseline values differed.
Clinical Relevance:
Changes in hydration status can cause alterations in plasma concentration of ANP, one of the hormones involved in the control of cardiovascular functions during exercise.