Ghrelin, a 28-amino-acid gut peptide is secreted from the stomach. It stimulates the release of growth hormone (GH) from the pituitary through GHS-R and plays important roles in energy homeostasis. In addition, ghrelin acts directly on the central nervous system to decrease sympathetic nerve activity. Ghrelin receptors (GHSRs) are concentrated in the hypothalamus-pituitary unit and may take the role of ghrelin in memory. GHSR is distributed in peripheral tissues, including the heart, lung, liver, kidney, pancreas, stomach, small and large intestines, adipose, and immune cells, suggesting that ghrelin has multiple functions in these tissues.