3.5 The vascular effects of BK-(1-9) fragments are not mediated by the activation of the kinin receptors
To assess the relevance of kinin receptors in the vasorelaxation of aortic ring preparations induced by BK-(1-9) fragments, we used pharmacological antagonists of either B1 and B2 receptors, respectively Lys-(des-Arg9-Leu8)-BK-(1-9) (100 nM) and HOE-140 (100 nM). The vasorelaxant effect induced by BK-(1-9) was abolished by antagonism of either B2 receptors (Figure 6A) or B1 receptors (Figure 6D). Interestingly, vasorelaxation induced by BK-(1-7) (Figures 6B and E) and BK-(1-5) (Figures 6C and F) were not altered in the presence of either antagonist of the kinin receptors.
The expression of mRNA for the kinin receptors was also assessed in rat thoracic aorta by qPCR. The mRNA for both B1 and B2 receptors were detected in the rat thoracic aorta, but the expression of B2 receptor mRNA was significantly higher than that of B1 receptor mRNA (Figure 6G). Taken together, the results indicate that the vasorelaxation of rat aortic rings induced by BK-(1-7) and BK-(1-5) was independent of the activation of B1 receptor and/or B2 receptors.