Plasma angiotensin-converting enzyme (ACE) concentration in Thoroughbred racehorses

Multi-species comparative analysis of the equine ACE gene identifies a highly conserved potential transcription factor binding site in intron 16

Angiotensin converting enzyme (ACE) is essential for control of blood pressure. The human ACE gene contains an intronic Alu indel (I/D) polymorphism that has been associated with variation in serum enzyme levels, although the functional mechanism has not been identified. The polymorphism has also been associated with cardiovascular disease, type II diabetes, renal disease and elite athleticism. We have characterized the ACE gene in horses of breeds selected for differing physical abilities. The equine gene has a similar structure to that of all known mammalian ACE genes. Nine common single nucleotide polymorphisms (SNPs) discovered in pooled DNA were found to be inherited in nine haplotypes. Three of these SNPs were located in intron 16, homologous to that containing the Alu polymorphism in the human. A highly conserved 18 bp sequence, also within that intron, was identified as being a potential binding site for the transcription factors Oct-1, HFH-1 and HNF-3β, and lies within a larger area of higher than normal homology. This putative regulatory element may contribute to regulation of the documented inter-individual variation in human circulating enzyme levels, for which a functional mechanism is yet to be defined. Two equine SNPs occurred within the conserved area in intron 16, although neither of them disrupted the putative binding site. We propose a possible regulatory mechanism of the ACE gene in mammalian species which was previously unknown. This advance will allow further analysis leading to a better understanding of the mechanisms underpinning the associations seen between the human Alu polymorphism and enzyme levels, cardiovascular disease states and elite athleticism.

Circulating angiotensin converting enzyme in endurance horses: effect of exercise on blood levels and its value in predicting performance

REASONS FOR PERFORMING STUDY

Investigate angiotensin converting enzyme (ACE) activity in equine plasma as a predictor of performance in endurance competitions and the effect of endurance exercise on ACE activity.

HYPOTHESIS

Precompetition values of ACE activity in equine blood are correlated with performance results and with heart rates pre- and post competition used as indicators of fitness. Endurance exercise increases ACE activity.

METHODS

Nineteen horses participating in an 80 km endurance competition had venous blood samples collected before and after the ride. ACE activity and total protein were measured in the blood samples and heart rates and finishing positions were recorded. Statistical analysis included paired t tests and Spearman's rank correlation coefficient.

RESULTS

Of the 19 horses enlisted, only 16 horses completed the ride. Of these 16, another 2 were disqualified at the last veterinary check. When the 16 horses were considered, precompetition heart rate, but not ACE, was correlated with finishing position. When only the 14 horses that were classified were considered, the association disappeared. ACE activity was similar before and after competition.

CONCLUSIONS

Precompetition ACE activity in endurance horses competing in an 80 km event was not associated with either finishing position or heart rates before or after competition, indicating that the enzyme is not a good predictor of performance in this form of equestrian competition. Endurance competition did not significantly alter ACE activity in this group of horses.

Determination of angiotensin I-converting enzyme activity in equine blood: lack of agreement between methods of analysis

Angiotensin-I converting enzyme (ACE) is a key regulator of blood pressure, electrolytes and fluid homeostasis through conversion of angiotensin I into angiotensin II. Recently, a genetic polymorphism of the ACE gene, which accounts for 47% of the variation of ACE activity in blood, has been advocated as a biomarker of athletic aptitude. Different methods of analysis and determination of ACE activity in plasma have been used in human and equine research without a consensus of a "gold standard" method. Different methods have often been used interchangeably or cited as being comparable in the existing literature; however, the actual agreement between assays has not been investigated. Therefore, in this study, we evaluated the level of agreement between three different assays using equine plasma obtained from 29 horses. Two spectrophotometric assays using Furylacryloyl-phenylalanyl-glycyl-glycine as substrate and one fluorimetric assay utilizing o-aminobenzoic acid-FRK-(Dnp)P-OH were employed. The results revealed that the measurements from the different assays were not in agreement, indicating that the methods should not be used interchangeably for measurement of equine ACE activity. Rather, a single method of analysis should be adopted to achieve comparable results and critical appraisal of the literature is needed when attempting to compare results obtained from different assays.

Clinical pathology in the racing horse: the role of clinical pathology in assessing fitness and performance in the racehorse

Clinical pathology is frequently used in racehorses to screen for "fitness" to race and to screen for disease that may affect performance. The role of clinical pathology in exercise testing of racehorses is important, especially in the area of blood lactate responses to exercise. This article discusses the use of resting and dynamic clinical pathology in the racehorse, especially in respect to investigation of the state of training (or fitness) and detection of subclinical performance-limiting disease.