Pharmacological characterization of neuropeptide Y-(2-36) binding to neuropeptide Y Y1 and Y2 receptors.

Neuropeptide Y-(2-36) has been reported by several research groups to be a more potent orexigenic agent than intact neuropeptide Y. Therefore, it has been proposed that a novel 'Y1 variant' may modulate ingestive behavior. To define the receptor subtype involved in neuropeptide Y-stimulated feeding behavior, we evaluated the binding properties of neuropeptide Y-(2-36) and [125I]neuropeptide Y-(2-36) in established neuropeptide Y1 and Y2 containing cell lines and tissues. Neuropeptide Y-(2-36) displaced [125I]peptide YY binding to SK-N-MC cells (neuropeptide Y Y1 receptors) with a Ki of 3.69 nmol and SK-N-BE(2) cells (neuropeptide Y Y2 receptors) with a Ki of 3.08 nmol. Neuropeptide Y-(2-36) also displaced [125I]peptide YY binding to rat cerebral cortex, hippocampus and olfactory bulb with similar affinities. To examine the brain distribution of [125I]peptide YY, [125I]neuropeptide Y and [125I]neuropeptide Y-(2-36), adjacent sections were labeled and the binding sites detected by autoradiography. A similar distribution of binding was observed for each radioligand in all regions examined. Therefore, neuropeptide Y-(2-36) binds non-selectively to neuropeptide Y Y1 and neuropeptide Y Y2 receptors, but with lower affinity than neuropeptide Y and peptide YY. The increased potency and selectivity seen with neuropeptide Y-(2-36) in feeding studies cannot be explained on the basis of a unique in vitro pharmacology.