Bradycardic effect of endothelial-specific bradykinin type-II receptors overexpression in mice: impact on blood pressure

Abstract Background/Introduction Polymorphisms of the gene encoding for the bradykinin type-II receptors (B2R) has been shown to decrease the expression of B2R and increased vascular resistance and blood pressure in humans. Purpose We aimed to study the role of endothelial B2R on systolic blood pressure (SBP) and heart rate (HR) using a novel mice model with endothelial-specific B2R overexpression (B2tg) as compared with transgene negative littermates (B2n) and on differential expression of proteins potentially relevant to vascular tension. Methods Human and murine B2R expression levels were quantified by rtPCR. Thoracic aortic tissues were used for vascular reactivity studies and proteomic analysis. SBP and HR were measured by the tail-cuff method at baseline, after administration of the COX inhibitor diclofenac (10 mg/kg/day), B2R antagonist icatibant (1 mg/kg) or NOS inhibitor L-NAME (100 mg/kg/day). Results In aortic tissues of B2tg human B2R were exclusively expressed (n=6, P=0.0005), while murine B2R expression levels remained unchanged. Similar results were found in skeletal muscle tissues used as an estimate for resistance vessels. Aortic ring studies revealed a concentration-dependent constriction to bradykinin in wild-type mice (maximal vasoconstriction 9.6±3.0%, n=5) whereas aortic rings of B2tg showed concentration-dependent relaxation (-27.4±4.1%, n=12). SBP was significantly lower in B2tg (125.0 ±1.6 mmHg) as compared to B2n (129.9±1.1 mmHg, n=9, P=0.03). Diclofenac treatment slightly but not significantly reduced SBP in B2n (to 125.5±2.4 mmHg, P=0.09) and in B2tg (to 119.8±2.8 mmHg, n=9, P=0.12), however the difference in SBP remained (P=0.03). In a pilot study, L-NAME administration did also not change the SBP difference between B2n and B2tg (9.9±10.3 mmHg, n=3-4). In contrast, icatibant administration abolished the difference between the groups (B2n 128.6±4.6 vs B2tg 128.3±2.0 mmHg, n=8, P=ns) suggesting the involvement of endothelial B2R in SBP reduction. Interestingly, in the same mice, HR was significantly lower in B2tg (571.4±20.8 bpm) as compared to B2n (626.7±13.7 bpm, P=0.02). While diclofenac didn’t affect HR, icatibant significantly increased HR to (630.8±21.8 bpm in B2tg and 685.5±16.4 bpm in B2n, n=8, P=0.01). Only in B2tg, there was a significant strong correlation between SBP and HR (r=0.76, P=0.016). Analysis of proteomic data revealed differential upregulation of proteins related to cell adhesion (CD44), extracellular matrix (hyaluronidase), and differential downregulation of proteins related to oxidative stress (superoxide dismutase) in B2tg. Conclusion Endothelial B2R overexpression reduces SBP and HR. SBP reduction is not dependent on two major vascular pathways stimulated by products of NOS and COX but appears to be related to endothelial B2R-dependent HR reduction. Hence, agonism at B2R could be a valuable target for development of new cardiovascular drugs.