Endothelial dysfunction might be involved in the pathogenesis of myxomatous mitral valve disease (MMVD) in dogs. A decreased plasma concentration of the nitric oxide metabolites nitrate and nitrite have been found in Cavalier King Charles Spaniels (CKCS) with mitral regurgitation, suggesting an endothelial dysfunction in dogs with MMVD. It is speculated that the vasodilator prostacyclin also plays a role in the pathogenesis of MMVD.
The aims of this study were to validate an enzyme immunoassay for a metabolite of canine prostacyclin (6-keto-prostaglandin(PG) F1α) and to compare plasma and urinary 6-keto-PGF1α in dogs with different degrees of MMVD.
The study included 76 privately owned dogs: 34 CKCS, 32 Dachshunds and 10 control dogs of different breeds not predisposed to MMVD. All dogs went through clinical and echocardiographic examination. The degree of MMVD was estimated by echocardiographic evaluation of the degree of mitral valve prolapse, mitral regurgitation and heart dimensions. Spontaneous urine samples were collected and blood was drawn from the jugular vein. 6-keto-PGF1α was measured in plasma and urine by enzyme immunoassay (Amersham 6-Keto-Prostaglandin F1α Enzymeimmunoassay Biotrack (EIA) System, GE healthcare). Two-way analyzes of variance (ANOVA) was used to test the influence of different MMVD parameters, body weight, age and gender on the urinary and plasma concentration of 6-keto-PGF1α in CKCS and Dachshunds. Wilcoxon signed ranks-tests were used to asses if the concentrations of 6-keto-PGF1α in the control dogs were different from concentrations in CKCS and Dachshunds.
The intra- and inter-assay coefficient of variation of the enzyme immunoassay was 5 % and 8 % at high concentrations of 6-keto-PGF1α, and 20 % and 24 % at low concentrations of 6-keto-PGF1α, respectively. The range of plasma and creatinine standardized urinary 6-keto-PGF1α concentration was 24.1-185.2 pg/ml and 77.2-732.2 pg/µmol urinary creatinine, respectively. The severity of MMVD, body weight, age and gender were not associated with plasma or urinary 6-keto-PGF1α, however the control dogs had a significantly lower creatinine standardized urinary 6-keto-PGF1α than the CKCS and Dachshunds.
In conclusion, the enzyme immunoassay seemed valid for measuring canine 6-keto-PGF1α in plasma and urine. Plasma or urinary 6-keto-PGF1α does not appear to be influenced by the degree of MMVD in CKCS or Dachshunds. However, the cause of lower creatinine standardized urinary 6-keto-PGF1α in control dogs compared to CKCS and Dachshunds remains to be established.