Peptide-YY and neuropeptide-Y inhibit vasoactive intestinal peptide-stimulated adenosine 3',5'-monophosphate production in rat small intestine: structural requirements of peptides for interacting with peptide-YY-preferring receptors

Previous binding studies indicated that peptide-YY (PYY) and neuropeptide-Y (NPY) shared a common PYY-preferring receptor site in rat small intestinal epithelium. We showed here that PYY and NPY inhibited vasoactive intestinal peptide (VIP)-stimulated cAMP production in epithelial cells isolated from rat small intestine and examined their structure-activity relationship. Inhibition of VIP-stimulated cAMP by PYY or NPY is time and dose dependent; half-maximal effects were observed for 10 and 107 nM, respectively. In contrast, the structurally related peptide, pancreatic polypeptide, was only active at 1 microM. PYY or NPY reduced the efficacy of VIP by about 50% without altering its potency. Both peptides also suppressed prostaglandin E1-, prostaglandin E2-, and forskolin-stimulated cAMP production and reduced basal cAMP levels. Their inhibitory effects were observed throughout the small intestine, including duodenum, jejunum, and ileum, but not in large intestine. PYY or NPY and epinephrine (through alpha 2-adrenergic receptors) did not exert additive inhibitory effects on intestinal cAMP production. Several fragments of PYY and NPY were used to characterize their structural requirement for inhibiting VIP-stimulated cAMP production and competing with 125I]PYY for binding to intestinal membranes. A highly significant correlation was observed between IC50 values measured in the two assays. No partial sequence of PYY retained the full activity of intact PYY, but the C-terminal portion of PYY was shown to be much more important than the N-terminal portion. Deletion of 21 amino acids from the N-terminus PYY-(22-36)] only resulted in a 4- to 5-fold decrease in potency compared to that of PYY-(1-36). In contrast, PYY-(27-36) exhibited a drastic loss of potency. The N-terminal fragments PYY-(1-22) and PYY-(1-28) also had very low potencies. Similar results were obtained with NPY fragments. These results provide the first insight on the negative coupling of PYY-preferring receptors with the cAMP production system in small intestine and evidence of the crucial role of the C-terminal portion of PYY in interaction with these receptors.