Prejunctional effects of angiotensin II and bradykinin in the heart and blood vessels

1 Angiotensin and bradykinin facilitate the release of noradrenaline from s ympathetic nerve terminals and cause positive inotropy in rat isolated atri a and ventricles. The effect of bradykinin was enhanced by the ACE inhibito r, ramiprilat. 2 The facilitated release of noradrenaline in rat ventricle by bradykinin w as blocked by the beta(2)-receptor antagonist HOE-140. This response is als o reduced by removing the endocardium, suggesting the release of a mediator from the endocardium. 3 The facilitated noradrenaline release by angiotensin II and bradykinin wa s blocked by the angiotensin receptor antagonist saralasin to the same exte nt. In contrast, losartan caused only minor blockade in a range of vascular and cardiac tissues. This suggests that angiotensin and bradykinin exert t hese responses by interacting with a prejunctional receptor different from the established AT(1) subtype. 4 These results suggest that bradykinin mediates facilitation of noradrenal ine release via the local release of angiotensin onto an atypical AT(1) rec eptor.