Neuromedin B (NMB) is a peptide agonist of the NMB receptor (Ki = 7.4 nM in NCI-H1299 small cell lung cancer cells expressing the human receptor). It displays similar affinity for frog [Phe13]bombesin receptors (Ki = 11 nM) and lower affinities for human gastrin-releasing peptide receptor and bombesin receptor subtype 3 (Kis = 440 and 4,800 nM, respectively). Intrathecal administration of NMB (0.1-1 nmol) induces dose-dependent itching behavior in mice. NMB (50 μg, s.c.) reduces serum thyroid stimulating hormone (TSH) by 30% in mice indicating a role in pituitary-thyroid axis function. In rodents, NMB is also involved in mediating stress and fear responses, thermoregulation, and can stimulate the contraction of the uterus and gastrointestinal smooth muscle.
