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Aim of this study was to analyze if the plasma levels of angiotensin-II, aldosterone, endothelin-1 and ANP can be used for early diagnosing and staging heart diseases and for providing prognostic information in horses with cardiac diseases before and after exercise. Therefore, 54 equine patients from the equine hospital of Freie Universität Berlin were examined. 15 horses had no evidence of cardiac disease (group one), 22 horses had evidence of cardiac disease with normal heart dimensions (group two) and 17 horses had evidence of cardiac disease with altered heart dimensions (group three). The plasma levels of angiotensin-II, aldosterone, endothelin-1 and ANP were detected by using commercial ELISA kits. The analyses were performed by a veterinary diagnostic laboratory.
Limitations observed in this study were the small number of horses and the number of horses in which additional diseases like orthopedic disorders or respiratory disease were diagnosed, which might have influenced the plasma levels of the blood parameters. Evaluation of exercise influence on blood parameters in horses with cardiac disease compared to horses without cardiac disease was limited by the lack of a standardized exercise protocol and by low exercise intensity.
All in all, the angiotensin-II, aldosterone and endothelin-1 plasma pre and post exercise levels did not differ significantly among the three groups. As a consequence, detection of plasma levels of angiotensin-II, aldosterone and endothelin-1 doesn´t seem to be useful for early diagnosing of cardiac diseases in horses. Also post exercise plasma levels of angiotensin-II, aldosterone and endothelin-1 don´t seem to give any beneficial information compared to conventional diagnostic methods. As opposed to this, the mean plasma ANP concentration pre and post exercise was lower in groups two and three compared to group one (CpANPR: group one: 76,3 ± 53,8 pg/ml, group two: 21,0 ± 52,3 pg/ml, group three: 14,9 ± 50,7 pg/ml; CpANPE: group one: 67,1 ± 43,0 pg/ml group two: 4,5 ± 10,4 pg/ml, group three: 8,6 ± 25,7 pg/ml). Whether the low ANP results in horses with heart disease are a consequence of cardiac disease can`t be concluded from this study. Further investigation is needed. Especially histopathological investigations have to clear if severe heart disease in horses can lead to degradation of ANP secreting cardiac myocytes and thus lead to low ANP plasma levels. Further investigation is also needed to determine to what extent the storage time of blood samples leads to depletion of equine ANP in the blood samples.
Although the plasma levels of endothelin-1 in horses with cardiac disease (groups two and three) were not significantly higher than the plasma levels of endothelin-1 in horses without cardiac disease (group one), a significant correlation could be observed between the plasma levels of endothelin-1 in group three and the left atrial diameter at rest as well as post exercise. This suggests a relation between the severity of disease and the ET-1 plasma levels. As for endothelin-1 a significant effect of weight, age and fitness level could be observed. Further investigation with more horses is needed to assess the beneficial effects of endothelin-1 in grading the severity of heart diseases. Thereby the above-mentioned effects on ET-1 should be noted.
Compared to conventional diagnostic methods like ultrasound, detection of plasma levels of angiotensin-II, aldosterone and ANP doesn´t seem to provide any further prognostic information or further information for staging cardiac diseases in horses.
However, further investigation is needed to conclusively assess the beneficial effects of angiotensin-II, aldosterone and endothelin-1 in diagnosing and grading the severity of cardiac diseases in horses. Also, further investigation is needed to conclusively assess the beneficial effects of angiotensin-II, aldosterone and endothelin-1 as a prognostic indicator in horses with cardiac diseases. Thereby the limitations observed in this study should be excluded.