The antinociceptive effects of spinally administered neuropeptide Y in the rat: systematic studies on structure-activity relationship.

Neuropeptide Y (NPY) is a 36-amino-acid, C-terminal amidated peptide that is found in bulbospinal pathways and can inhibit the release of the primary afferent C-fiber neurotransmitter, substance P. Based on these observations, the present studies examined the possible antinociceptive effects of this peptide and several NPY fragments after intrathecal administration in rats prepared with chronic intrathecal catheters. In the 52 degrees C hot plate test, NPY produced a dose-dependent elevation in the nociceptive threshold with a median effective dose of 1.1 nmol. The ordering of fragments' activity was: NPY greater than NPY16-36 greater than or equal to NPY19-36 greater than or equal to NPY14-36 greater than or equal to NPY18-36 much greater than NPY1-36-OH = NPY18-36-OH = 0. In the paw pressure test, NPY was not active, even at the highest doses examined (median effective dose greater than 20 nmol), whereas the C-terminal fragments retained their potency and produced significant increases in the pressure required to evoke escape (NPY18-36: median effective dose = 18.7 nmol). The rank ordering of activity in the paw pressure test was: NPY19-36 greater than or equal to NPY14-36 greater than or equal to NPY18-36 greater than or equal to NPY16-36 much greater than NPY = NPY18-36-OH = 0. Peptide YY, human pancreatic polypeptide and avian pancreatic polypeptide behave similarly to NPY.(ABSTRACT TRUNCATED AT 250 WORDS)