J Vet Sci.  2011 Mar;12(1):21-25. 10.4142/jvs.2011.12.1.21.

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

• Costa MF
• Carmona AK
• Alves MF
• Ryan TM
• Davies HM
• Anderson G
• Slocombe R

• KMID: 1067333
• DOI: http://doi.org/10.4142/jvs.2011.12.1.21

Abstract

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.

Keyword

angiotensin I-converting enzyme; assay agreement; biochemistry; equine; methodology

MeSH Terms

Animals
Enzyme Assays/*methods
Female
Fluorometry/*methods
Horses/blood/genetics/*metabolism
Male
Oligopeptides/pharmacology
Peptidyl-Dipeptidase A/blood/genetics/*metabolism
Polymorphism, Genetic
Reference Values
Spectrophotometry/*methods

Figure

• 

  Fig. 1 Bland and Altman plot showing the limits of agreement (two outer lines), 95% confidence interval of the mean difference (two lines on either side of the mean) and the mean difference between the furylacryloyl-phenylalanyl-glycyl-glycine (FAPGG) method and the angiotensin I-converting enzyme Infinity (ACEIn) method. n = 29.

• 

  Fig. 2 Bland and Altman plot showing the limits of agreement (two outer lines), 95% confidence interval of the mean difference (two lines on either side of the mean) and the mean difference between the furylacryloyl-phenylalanyl-glycyl-glycine (FAPGG) method and the o-aminobenzoic acid-FRK(Dnp)P-OH (ABZ) method. n = 29.

• 

  Fig. 3 Bland and Altman plot showing the limits of agreement (two outer lines), 95% confidence interval of the mean difference (two lines on either side of the mean) and the mean difference between the o-aminobenzoic acid-FRK(Dnp)P-OH (ABZ) method and angiotensin I-converting enzyme Infinity (ACEIn) method. n = 29.

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