Effects of two training protocols on Angiotensin I-converting enzyme (ACE) activity in horses

High-volume endurance exercise training stimulates hematopoiesis by increasing ACE NH2-terminal activity

One of the health benefits of endurance exercise training (ET) is the stimulation of hematopoiesis. However, the mechanisms underlying ET-induced hematopoietic adaptations are understudied. N-Acetyl-Seryl-Aspartyl-Lysyl-Proline (Ac-SDKP) inhibits proliferation of early hematopoietic progenitor cells. The angiotensin I-converting enzyme (ACE) NH2-terminal promotes hematopoiesis by inhibiting the anti-hematopoietic effect of Ac-SDKP. Here we demonstrate for the first time the role of ACE NH2-terminal in ET-induced hematopoietic adaptations. Wistar rats were subjected to 10 weeks of moderate-(T1) and high-(T2) volume swimming-training. Although both protocols induced classical ET-associated adaptations, only T2 increased plasma ACE NH2-domain activity (by 40%, P=0.0003) and reduced Ac-SDKP levels (by 50%, P<0.0001). T2 increased the number of hematopoietic stem cells (HSCs; ∼200%, P=0.0008), early erythroid progenitor colonies (∼300%, P<0.0001) and reticulocytes (∼500%, P=0.0007), and reduced erythrocyte lifespan (∼50%, P=0.022). Following, Wistar rats were subjected to T2 or T2 combined with ACE NH2-terminal inhibition (captopril (Cap) treatment: 10 mg.kg-1.day-1). T2 combined with ACE NH2-terminal inhibition prevented Ac-SDKP decrease and attenuated ET-induced hematopoietic adaptations. Altogether, our findings show that ET-induced hematopoiesis was at least partially associated with increased ACE NH2-terminal activity and reduction in the hematopoietic inhibitor Ac-SDKP.

Expression of select mRNA in Thoroughbreds with catastrophic racing injuries

BACKGROUND

The ability to identify horses at risk for catastrophic injuries continues to be a pressing issue for the racing industry, especially given recent events in North America.

OBJECTIVES

Since most catastrophic injuries occur in areas of existing pathology and this pathology is likely to elicit an inflammatory response, it was hypothesised that analysis of messenger RNA (mRNA) expression would detect significant changes in select genes in horses at risk for a catastrophic injury.

STUDY DESIGN

Prospective cohort study.

METHODS

Five racing jurisdictions across the United States participated in this study. A total of 686 Tempus^® RNA Blood Tube samples were collected for mRNA analysis from 107 catastrophically injured horses, as well as from noninjured horses sampled either prerace (n = 374) or postrace (n = 205). A subset of horses (n = 37) were sampled both prerace and postrace for analysis of expression changes during the postrace period.

RESULTS

Of 21 genes analysed via RT-qPCR, the expression of 12 genes (ALOX5AP, CD14, IL-10, IL-1β, IL-6, IL-8, MMP1, PTGS2, TLR4, TNFα, TNFSF13B and VEGFA) changed significantly within 45 minutes after a race and were excluded. Of the remaining nine genes (BMP-2, IGF-1, IL1RN, MMP2, MMP9, Osteoprotegrin, RANKL, SAA1 and TGFβ), three genes (IGF-1, IL1RN and MMP2) were found to be significantly different between catastrophically injured and noninjured horses using multiple logistic regression modelling. Receiver operating characteristic analysis of models, which included mRNA expression, demonstrated sensitivities from 76%-82% (95% CI: 67%-93%) and specificities from 84%-88% (95% CI: 71%-94%) at the Youden Index.

MAIN LIMITATIONS

Samples were collected as soon as possible postinjury (within 30 minutes).

CONCLUSIONS

Analysis of mRNA expression of specific genes in the future may be considered as an economical, accessible and noninvasive means by which horses at risk for catastrophic injury can be identified.

ACE activity post-race is influenced by furosemide administration

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.