Neuromedin U-23 (NMU-23) is a neuropeptide involved in diverse biological processes, including smooth muscle contraction, energy homeostasis, and nociception.1It is an agonist of neuromedin-U receptor 1 (NMUR1; EC50= 0.17 nM for the human receptor in a calcium mobilization assay using HEK293 cells) and NMUR2 (EC50= ~1.4-2 nM for arachidonic acid release in CHO cells expressing the human receptor).2,3NMU-23 (1 μM) induces contractions in isolated rat colon smooth muscle strips.4It decreases body weight and food intake and increases core body temperature in mice when administered at a dose of 36 μg/animal.5Intrathecal administration of NMU-23 decreases the mechanical pain threshold in the von Frey test in rats.6 1.Mitchell, J.D., Maguire, J.J., and Davenport, A.P.Emerging pharmacology and physiology of neuromedin U and the structurally related peptide neuromedin SBr. J. Pharmacol.158(1)87-103(2009) 2.Szekeres, P.G., Muir, A.I., Spinage, L.D., et al.Neuromedin U is a potent agonist at the orphan G protein-coupled receptor FM3J. Biol. Chem.275(27)20247-20250(2000) 3.Hosoya, M., Moriya, T., Kawamata, Y., et al.Identification and functional characterization of a novel subtype of neuromedin U receptorJ. Biol. Chem.275(38)29528-29532(2000) 4.Brighton, P.J., Wise, A., Dass, N.B., et al.Paradoxical behavior of neuromedin U in isolated smooth muscle cells and intact tissueJ. Pharmacol. Exp. Ther.325(1)154-164(2008) 5.Peier, A., Kosinski, J., Cox-York, K., et al.The antiobesity effects of centrally administered neuromedin U and neuromedin S are mediated predominantly by the neuromedin U receptor 2 (NMUR2)Endocrinology150(7)3101-3109(2009) 6.Yu, X.H., Cao, C.Q., Mennicken, F., et al.Pro-nociceptive effects of neuromedin U in ratNeuroscience120(2)467-474(2003)