Sodium ions attenuate the inhibitory effects of neuropeptide Y on norepinephrine release in rat hypothalamus

Neuropeptide Y (NPY) has a wide and specific distribution both in the central and peripheral nervous systems. In the present study, we have investigated the effects of NPY on norepinephrine release in rat hypothalamus, and further examined the interaction of NPY with α2-adrenergic receptors, as well as the influence of sodium ions on the modulation of norepinephrine release. In an in vitro study, NPY significantly inhibited the stimulation-evoked norepinephrine release from hypothalamic slices in a dose-dependent manner. The α2-adrenergic receptor agonist, UK 14,304, also reduced the stimulation-evoked norepinephrine release. A low concentration of NPY, which had no effects on its own, significantly potentiated the inhibitory effect of UK 14,304 on the stimulation-evoked [3H]norepinephrine release. The blockade of α2-adrenergic receptors by RX 781094 diminished the inhibitory effects of NPY on norepinephrine release. Pretreatment of slices with pertussis toxin (a potent inhibitor of the Gi-proteins) significantly attenuated the suppressive effects of NPY and UK 14,304 on norepinephrine release. When the sodium concentration of the perfusion medium was increased, the inhibitory effects of NPY and UK 14,304 on norepinephrine release were significantly reduced. These results show that NPY might inhibit norepinephrine release that is partially mediated by α2-adrenergic receptors and the pertussis toxin-sensitive Gi-proteins in rat hypothalamus. Moreover, less suppressive effects of NPY and UK 14,304 on norepinephrine release in the presence of excess sodium ions suggest that sodium ions might actively participate in regulating the NPY and α2-adrenergic receptor mediated functions in the central nervous system.