Effects of bradykinin on [3H]-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 [3H]-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 1 x 10(-6) mol/L 1.039 +/- 0.018, n = 6, P < 0.05; bradykinin 3.3 x 10(-6) mol/L 1.130 +/- 0.064, n = 6, P < 0.05). The basal release of [3H]-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.