Comparison between the actions of avian pancreatic polypeptide, neuropeptide Y and norepinephrine on the excitability of rat supraoptic vasopressin neurons.

Effects of pressure-applied avian pancreatic polypeptide (APP), neuropeptide Y (NPY) and norepinephrine (NE) on the activity of putative vasopressin-synthesizing neurosecretory cells of the supraoptic nucleus were studied in pentobarbitone-anesthetized male rats. APP (17-170 microM) excited 80% (20/25), NPY (20 microM-2 mM) excited 23% (6/26) and NE (100-200 microM) excited 76% (26/34) of cells tested; no depressant actions were observed. However, simultaneously applied APP appeared to reduce the NE-evoked excitation in 4/4 cells tested. These data indicate that an endogenous pancreatic polypeptide-like peptide may mimic the excitatory actions of NE on supraoptic vasopressin-synthesizing neurosecretory cells but only at high concentrations. These peptides do not potentiate but rather appear to interfere with NE's excitatory effects.