However, it is worth mentioning that the serum ET-1 level in BA patients with concomitant EH stage I was slightly increasing as BP value (and airway narrowing) was becoming normalized. It might be due to the fact that duration of treatment course was short. Consequently, there was not enough time spent between two examination points (before and after treatment). Moreover, it is known  that in human ET-1 mediates its bronchoconstrictive effect via B-type receptors (ЕТв). When ET-1 acts on ЕTв receptors it mainly induces vasorelaxation rather than vasoconstriction as compared with signaling via ЕTа receptors . Previously there was shown that in experimental conditions chronic hypoxia is characterized with enhanced ET-1-mediated signaling via ЕTв receptors that leads not only to bronchoconstriction but vasorelaxation as well . It is possible that patients with combined pathology might have increased ET-1 level at some stages that could be accompanied with vasorelaxation. It is supported by the evidence that BA patients with concomitant EH (Group III + IV) were found to have an inverse correlation between ET-1 level after treatment and BP values, in particular, systolic (r=-0.38, p=0.036) as well as diastolic (r=-0.38, p=0.037).
Conclusion. We have found that in BA patients ET-1 level in blood serum was dependent not only on the course of the respiratory disease, but also it was affected by accompanying cardiovascular pathology. After treatment of BA exacerbation patients with concomitant EH stage I were shown to have a higher serum level of endothelin-1 as compared with patients who had normal or optimal BP values.
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