EFFECTS OF BRADYKININ ON [H-3] NOREPINEPHRINE RELEASE IN RAT HYPOTHALAMUS

1. We examined the regulatory actions of bradykinin on norepinephrine release in the hypothalamus of rats. 2. Bradykinin increased the stimulation-evoked [H-3]norepinephrine release from hypothalamic slices of Sprague-Dawley rats in a dose-dependent manner (1 Hz:S2/S1 ratio, mean+/-s.e.m., control 0.868+/-0.016, n = 6; bradykinin 1X10(-6) mol/L 1.039+/-0.018, n = 6, P<0.05; bradykinin 3.3X10(-6) mol/L 1.130+/-0.064, n = 6, P<0.05). The basal release of [H-3]-norepinephrine was not affected by the peptide. 3. Bay K 8644, a dihydropyridine-sensitive calcium channel agonist, significantly potentiated the facilitatory effect of bradykinin on norepinephrine release, although Bay K 8644 by itself had no significant effect. By contrast, nicardipine, a dihydropyridine-sensitive calcium channel blocker, reversed the increase in norepinephrine release induced by bradykinin and Bay K 8644. 4. These results indicate that bradykinin may increase norepinephrine release in rat hypothalamus, partially mediated by interactions with dihydropyridine-sensitive calcium channels.