Synergistic effects of Bay K 8644 and bradykinin on norepinephrine release in the hypothalamus of spontaneously hypertensive rats.

1. In the present study, we examined the effects of Bay K 8644, a dihydropyridine (DHP)-sensitive Ca2+ channel agonist, and bradykinin on norepinephrine release in the hypothalamus of spontaneously hypertensive rats (SHR). 2. In the preliminary studies using Sprague-Dawley rats, Bay K 8644 by itself had no significant effects on the stimulation-evoked [3H]-norepinephrine release from hypothalamic slices. Bradykinin increased the stimulation-evoked [3H]-norepinephrine release in a dose-related fashion. The facilitatory effects of bradykinin on norepinephrine release were potentiated by Bay K 8644. 3. In SHR, Bay K 8644 significantly increased the stimulation-evoked norepinephrine release from hypothalamic slices. However, exposure of slices to Bay K 8644 caused no significant effects on norepinephrine release in Wistar-Kyoto (WKY) rats. The effects of Bay K 8644 in combination with bradykinin on the stimulation-evoked norepinephrine release were also greater in SHR than in WKY rats. 4. These results demonstrate that Bay K 8644 significantly potentiated the facilitatory effects of bradykinin on norepinephrine release in rat hypothalamus. The finding indicates a possible interaction of bradykinin with DHP-sensitive Ca2+ channels in the central nervous system. Furthermore, the pronounced effects of Bay K 8644 and bradykinin in SHR suggest that bradykinin-related Ca2+ channels might have a role in the regulation of norepinephrine release in the hypothalamus of SHR.