Ghrelin is a 28 residue pepetide expressed by stomach cells that is responsible for the hunger sensation. Expression is increased during times of fasting, and decreased after food consumption. Ghrelin is initially derived from a preprohormone called preproghrelin, which also generates a second peptide called obestatin. Obestatin is an endogenous ligand for the orphan G protein-coupled receptor GPR39 and is involved in satiety and decreased food intake. Ghrelin antibodies are useful tools for lipid and metabolism research as well as neuroscience studies.