Effect of exercise, phenylbutazone, and furosemide on the plasma renin activity and angiotensin I in horses.

The research studied the influences of exercise, phenylbutazone, and furosemide on plasma renin activity (PRA) and angiotensin I levels in racehorses. It identified an increase in the concentrations of PRA and angiotensin I after racing, with different reactions observed in horses that received prerace medication.

Background

• The study aimed to determine how exercise and certain medications (phenylbutazone, and furosemide) influence the circulating concentrations of two distinct hormones, angiotensin I and plasma renin activity (PRA), in racehorses.
• The hormones examined are part of the renin-angiotensin system, which regulates blood pressure and fluid balance in the body.

Methodology

• The study observed 45 Thoroughbred horses at different times: at rest, before racing with pre-racing medication, immediately after racing, and 1-2 hours after racing.
• Angiotensin I was measured using radioimmunoassay, a common technique for detecting and quantifying specific substances in the blood.
• PRA was calculated based on the rate of angiotensin I generation in plasma kept at 37 degrees Celsius.

Key Findings

• The study observed a marked increase in angiotensin I and PRA levels from rest to immediately post-race. However, this increase was less pronounced in anhidrotic horses.
• Administering furosemide before racing caused an increase in PRA levels while administering phenylbutazone led to a decrease.
• Remarkably, there were no significant increases in angiotensin I and PRA levels when horses had been given both furosemide and phenylbutazone as prerace medication.

Implications

• The results show that the physiological responses associated with intense exercise in horses include changes in levels of PRA and angiotensin I.
• This study suggests it influences the blood pressure and fluid balance in horses, contributing to their overall performance during a race.
• The findings could help guide the use of medications like furosemide and phenylbutazone in racehorses, particularly regarding timing and combination, for optimal effects.