Structure-function studies on neuropeptide Y and pancreatic polypeptide — evidence for two PP-fold receptors in vas deferens

Abstract

The biological effects of neuropeptide Y (NPY), rat pancreatic polypeptide (rPP), hybrid analogs of NPY and PP, and C-terminal fragments of NPY were studied in the field-stimulated rat vas deferens model. The results were correlated with paptide binding experiments in Y 1 and PP receptor assays on rat PC-12 cells and Y 2 receptors on porcine hippocampal membranes. NPY and rPP inhibited the electrically induced contractions in the vas deferens with an IC 50 of 25 and 22 nM respectively. However, in contrast to NPY, rPP could not totally block muscle activity. The inhibitory action of the long C-terminal fragments of NPY, NPY-(19–36) and NPY-(11–36), indicated that NPY acts through a Y 2 receptor in the vas deferens. The structural basis for the differential recognition of NPY and PP by Y 2 receptors and partly also by PP receptors, could be defined with hybrid analogs of PP and NPY. The analogs, [Ile 31,Gln 34]PP and [Leu 31,Pro 33]NPY reacted in the vas deferens preparation in accordance with their relative potency in the Y 2 and PP receptor assays. [Ile 31,Gln 34]PP, which bound to the Y 2 receptor like NPY, was also able to block the part of the contractile response which was resistant to rPP. It is concluded that in the vas deferens, PP-fold peptides act through two types of receptors: Y 2 and PP, and that residues in the C-terminal part of the molecules determine the differential recognition of the peptides by these receptor types.