ACE activity post-race is influenced by furosemide administration

Abstract

Exercise induced pulmonary haemorrhage (EIPH) affecting racehorses continues to raise questions regarding animal welfare and to-date no effective treatment has been identified. The mode of action of furosemide on EIPH, the only medication for the condition accepted in some racing jurisdictions, has not been completely elucidated. This research investigated the interaction between furosemide on angiotensin converting enzyme (ACE) as a potential pathway for future investigation of EIPH treatment options in a prospective case-control analytical study. ACE is a potent vasoconstrictor and substances reducing its activity could potentially contribute to decreasing blood pressure and EIPH. Horses racing on 8 official race days at Gávea Racetrack, Brazil had respiratory endoscopy data and blood samples collected after the race and were grouped into furosemide medicated and non-furosemide medicated horses. ACE measurement was conducted using fluorescence in a previously validated method. Environmental, race and haematological data were also recorded. A multiple regression model was used to analyse the data collected, with further analysis including Fisher’s exact test and Pearson’s chi-squared test with Yates’ continuity correction; a Welch two sample t-test and a simple linear regression model. 73 horses were included in the study. ACE activity between horses not medicated and medicated with furosemide was significantly different. Pre-race furosemide significantly influenced ACE activity post-race, while distance raced, temperature, humidity, and haematocrit did not. Horses medicated with pre-race furosemide still demonstrated some degree of bleeding after the race and were at higher risk of presenting EIPH than non-medicated horses. Horses medicated with furosemide have lower circulating ACE activity which might indicate a protective effect of furosemide. Furosemide might reduce EIPH severity after a single bout of exercise, but it does not abolish or reduce its occurrence.