Neuropeptide Y (NPY) elicits food intake through the action of hypothalamic G-protein-coupled receptors. Previous publications indicate that the Y5 receptor may represent one of these postulated hypothalamic "feeding" receptors. Using a potent and orally available Y5 antagonist L-152,804, we evaluated the involvement of the Y5 receptor in feeding regulation. L-152,804 displaced [I-125]peptide YY (PYY) binding to human and rat Y5 receptors with K-i values of 26 and 31 nM, respectively, and inhibited NPY (100 nM)-induced increase in intracellular calcium levels via human Y5 receptors (IC50 = 210 nM). L-152,804 did not show significant affinity for human Y1, Y2, and Y4 receptors at a dose of 10 mu M. Intracerebroventricular (ICV) (30 mu g) or oral (10 mg/kg) administration of L-152,804 significantly inhibited food intake evoked by ICV-injected bovine pancreatic peptide (bPP, 5 mu g; a moderately selective Y4, Y5 agonist) in satiated SD rats. However L-152,804 did not significantly inhibit ICV NPY (5 mu g; a Y1, Y2, Y5 agonist)-induced food intake. These findings suggest that L-152,804 is a selective and potent nonpeptide Y5 antagonist with oral bioavailability and brain penetrability. In addition, the anorexigenic effects of L-152,804 on bPP-induced feeding revealed participation of the Y5 receptor in feeding regulation, while ICV administration of NPY does not appear to significantly contribute to Y5 stimulated food intake. We conclude that the potent and orally active Y5 antagonist, L-152,804, represents a useful tool to address the physiological role of the Y5 receptor.