An endogenous hypothalamic neuropeptide hormone and agonist at MCH receptors; binds to human MCH1 and MCH2 receptors (IC50s = 0.17 and 2.9 nM, respectively); stimulates calcium accumulation in cells stably expressing human MCH1 and MCH2 (EC50s = 28 and 50 nM, respectively); binds to the rat MCH1 receptor (Ki = 0.16 nM), stimulates calcium accumulation (EC50 = 1.79 nM), and inhibits forskolin-induced intracellular cAMP accumulation (EC50 = 0.46 nM); binds to mouse MCH receptors on melanoma B16 cells (Ki = 33 nM) and dose-dependently activates the MAPK signaling pathway; increases cumulative food intake in rats (5 nmol/kg, i.c.v.)