Bradykinin increases BP in endotoxemic rat: functional and biochemical evidence of angiotensin II AT1/bradykinin B2 receptor heterodimerization

Abstract

Background and Purpose: Bradykinin may induce vasoconstriction in selected vessels or under specific experimental conditions. We hypothesized that inflammatory stimuli, such as endotoxin challenge, may induce the dimerization of AT1/B2 receptors, altering the vascular effects of bradykinin. Experimental Approach: Wistar rats received LPS (1 mg·kg−1, i.p.) and were anaesthetized for assessment of BP. Mesenteric resistance arteries were used in organ baths and subjected to co-immunoprecipitation and Western blot analyses. Key Results: At 24 and 48 hr after LPS, bradykinin-induced hypotension was followed by a sustained increase in BP, which was not found in non-endotoxemic animals. The B2 receptor antagonist Hoe-140 fully blocked the responses to bradykinin. The pressor effect of bradykinin was not prevented by prazosin, an α1-adrenoceptor antagonist, but it was inhibited by the AT1 receptor antagonist losartan or the Rho-kinase inhibitor Y-27632. Endotoxemic rats also displayed enhanced pressor responses to angiotensin II, which were blocked by Hoe-140. Co-immunoprecipitation isolated using anti-B2 or anti-AT1 receptor antibodies showed that resistance arteries presented augmented levels of the AT1/B2 receptor complexes at 24 hr after LPS injection. The presence of AT1/B2 receptor heterodimers did correlate with the development of losartan-sensitive contractile responses to bradykinin and potentiation of angiotensin II-induced contraction, which was prevented by Hoe-140. Conclusions and Implications: Endotoxin challenge is a stimulus for AT1/B2 receptor heterodimerization in native vessels and shifts the B2 receptor-dependent vascular effect of bradykinin to a more complex pathway, which also depends on AT1 receptors and their intracellular signalling pathways.