Regulation of neuropeptide Y release by neuropeptide Y receptor ligands and calcium channel antagonists in hypothalamic slices

Neuropeptide Y (NPY) is an important regulator of energy balance in mammals through its orexigenic, antithermogenic, and insulin secretagogue actions. We investigated the regulation of endogenous NPY release from rat hypothal amic slices by NPY receptor ligands and calcium channel antagonists. High-p otassium stimulation (60 mM) of the slices produced a calcium-dependent thr eefold increase in NPY release above basal release. The Y2 receptor agonist s NPY(13-36) and N-acetyl[Leu(28), Leu(31)]NPY(24-36), the Y4 agonist rat p ancreatic polypeptide (rPP), and the Y4/Y5 agonist human pancreatic polypep tide (hPP) significantly reduced both basal and stimulated NPY release. NPY (13-36)-induced reduction of NPY release could be partially prevented in th e presence of the weak Y2 antagonist T4-[NPY(33-36)](4), whereas the hPP- a nd rPP-induced inhibition of release was not affected by the Y5 antagonist CGP71683A, or the Y1 antagonist BIBP3226. The selective Y1, Y2, and Y5 anta gonists had no effect on either basal or potassium-stimulated release when administered alone. The calcium channel inhibitors omega-conotoxin GVIA (N- type), omega-agatoxin TK (P/Q-type), and omega-conotoxin MVIIC (Q-type) all significantly inhibited potassium-stimulated NPY release, without any effe ct on basal release, whereas nifedipine had no effect on either basal or st imulated release. Addition of both omega-conotoxin GVIA and omega-agatoxin TK together completely inhibited the potassium-stimulated release. In concl usion, we have demonstrated that NPY release from hypothalamic slices is ca lcium-dependent, involving N-, P-, and Q-type calcium channels. NPY release is also inhibited by Y2 agonists and rPP/hPP, suggesting that Y2 and Y4 re ceptors may act as autoreceptors on NPY-containing nerve terminals.