Does Plasma ACE Level Accurately Reflect the Occurrence of Exercise‐Induced Pulmonary Haemorrhage?

Abstract

IntroductionExercise‐induced pulmonary haemorrhage (EIPH) is a highly prevalent airway disorder responsible for poor‐performance in horses. While various methodologies are available for diagnosing EIPH, no readily available systemic biomarker has to date been definitively validated. A recent study demonstrated that angiotensin‐converting enzyme (ACE) activity in plasma was increased in horses with higher degrees of haemorrhage, as assessed by post exercise tracheal endoscopy.AimsTo investigate plasma ACE activity in horses suffering previous episodes of EIPH and controls.MethodsVenous blood samples were collected at rest from 121 client‐owned, racing or race‐fit Standardbred racehorses. Bronchoalveolar lavage fluid (BALF) samples were collected from right and left lung, cytocentrifuged and stained with Perl's Prussian blue. Total haemosiderin scores (THS) were calculated for detecting EIPH. According to THS, 36 horses were diagnosed with EIPH and 85 were assigned as controls. The ACE levels were determined on an automated spectrophotometer, using FAPGG as a substrate.ResultsPlasma ACE levels in EIPH‐affected horses (85.1 ± 24.6 u/l) were lower than those of control horses (94.4 ± 24.0 u/l), even if the tendency was not statistically significant (P = 0.056). Within each group of horse (EIPH and control), no significant difference was found for THS between lungs; a significant correlation between right and left BALF being furthermore observed (R = 0.643; P<0.001). No significant correlation was however found between plasma ACE levels and THS of BALF from either left or right lung.Conclusions and practical significanceThis is the first study determining plasma ACE activity in a large population of racehorses at training. Apart from acute pulmonary haemorrhage, these results highlight that previous episodes of EIPH might be associated with a moderate decrease of circulating ACE levels. Further studies are warranted to establish the precise implication of ACE in the physiopathology of EIPH and determine its relevance as a systemic biomarker.Ethical animal researchThis study has been approved by the Regional Animal Ethic Committee and all owners gave consent. Sources of funding: I.F.C.E. (French National Studs) and S.E.C.F. (French Trotters Racing Association). Competing interests: None.