Plasma renin activity and aldosterone and vasopressin concentrations during incremental treadmill exercise in horses.

The research study involves the examination of how incremental treadmill exercise impacts the activity of plasma renin, and the concentration of plasma aldosterone and arginine vasopressin in six untrained mares. The findings indicate that all three measured conditions increased with exercise intensity, with heart rate and plasma renin activity reaching plateau at certain speed.

Study Setup

• The study involved six untrained mares that were subjected to incremental treadmill exercise. The treadmill was set on a 6-degree slope with an initial speed of 4 m/s. The speed was increased by 1 m/s every minute.
• The researchers measured plasma renin activity, plasma aldosterone and plasma arginine vasopressin concentrations, and heart rate at each step of the exercise test.
• Once obtained, the plasma was stored at -80 C for later analysis using radioimmunoassay to determine the different hormone concentrations.

Results and Observations

• Exercise led to a significant increase in heart rate, from an average of 40 beats/minute at rest to 206 beats/minute at the speed of 9 m/s.
• Plasma renin activity also increased from 1.9 ng/ml/h at rest to 5.2 ng/ml/h at the speed of 9 m/s. This change paralleled the changes observed in heart rate.
• Strong linear correlations were identified between exercise intensity (and duration) and heart rate and plasma renin activity up to a treadmill speed of 9 m/s.
• Both heart rate and plasma renin activity reached a plateau and did not increase further when the speed was raised from 9 m/s to 10 m/s.
• Plasma aldosterone concentration increased from 48 pg/ml at rest to 191 pg/ml at a speed of 10 m/s, with a linear correlation identified between exercise intensity (and duration) and aldosterone concentration.

Conclusion

• The results of the study implied an increase in plasma renin activity and plasma aldosterone and plasma arginine vasopressin concentrations with increased exercise intensity in untrained mares.
• However, it was observed that the heart rate and plasma renin activity did not increase beyond a certain speed, suggesting a limit or plateau in these bodily responses to exercise intensity.