BRADYKININ B-2-RECEPTOR-MEDIATED STIMULATION OF EXOCYTOTIC NORADRENALINE RELEASE FROM CARDIAC SYMPATHETIC NEURONS

Myocardial ischemia, as well as angiotensin-converting-enzyme-inhibito rs increase cardiac concentrations of the non-apeptide bradykinin. Car diac effects of bradykinin are potentially mediated by modulation of s ympathoadrenergic neurotransmission. Accordingly, the present study wa s designed to examine the influence of bradykinin on exocytotic noradr enaline release from rat isolated perfused heart. Exocytotic noradrena line release was induced by electrical field stimulation (1 min, 5 V, 6 Hz) twice to compare the effect of intervention (S-2) with respectiv e control stimulation (S-1). The overflow of endogenous noradrenaline was determined by high pressure liquid chromatography and electrochemi cal detection. The results are expressed as the mean S,IS, ratio +/- S .E.M. Bradykinin (1 mu mol/l) evoked a significant increase in noradre naline release (S-2/S-1: 1.60+/-0.12; P<0.01), which was even more pro nounced after inhibition of neuronal reuptake of noradrenaline by desi pramine (0.1 mu mol/l: S-2/S-1: 1.83+/-0.15; P<0.01) excluding interfe rence of bradykinin with the noradrenaline uptake(1) carrier. The conc entration-response curve for bradykinin (0.1 nmol/l to 10 mu mol/l) re vealed a maximum effect at 1 mu mol/l and an EC50-value of 7.5 nmol/l. The effect of bradykinin was unaltered by the B-1-receptor antagonist des-Arg(9) (Leu(8))-bradykinin (1 mu mol/l: S-2/S-1: 1.69+/-0.17), wh ereas it was reduced significantly by the B-2-receptor antagonist Hoe 140 (1 mu mol/l; S-2/S-1: 1.14+/-0.11; P<0.05). Des-Arg(9)-bradykinin (1 mu mol/l), a specific B-1-agonist, had no effect on stimulation-ind uced noradrenaline release (S-2/S-1: 0.94+/-0.08). Utilizing pharmacol ogical interventions, we attempted to characterize the intraneuronal s ignal transduction pathway mediating the effect of bradykinin on exocy tosis. Neither inhibition of cyclooxygenase nor blockade of nitric oxi de synthesis affected bradykinin-induced stimulation of noradrenaline release. Likewise, inhibition of protein kinase C by bisindolylmaleimi de (1 mu mol/l) or tyrosine kinase by genistein (10 mu mol/l) had no e ffect on the promoting action of bradykinin. In contrast, inhibition o f cytosolic phospholipase A(2) activity by the specific inhibitor AACO CF(3) (1 mu mol/l) prevented bradykinin-induced increase in noradrenal ine release (S-2/S-1: 1.09+/-0.15; P<0.01). In conclusion, bradykinin increases exocytotic release of endogenous noradrenaline from cardiac sympathetic neurons via activation of presynaptic B-2-receptors. Intra neuronal coupling of B-2-receptors to phospholipase A(2) appears to me diate the facilitatory effect of bradykinin on noradrenaline release i n rat heart. (C) 1997 Academic Press Limited.