Endocrine and non-endocrine actions of ghrelin.

Ghrelin is a 28-amino-acid peptide predominantly produced by the stomach. Substantially lower amounts were detected in bowel, pancreas, kidneys, the immune system, placenta, testes, pituitary, and hypothalamus. Ghrelin displays strong growth hormone (GH)-releasing action mediated by the activation of the so-called GH secretagogue (GHS) receptor (GHS-R) type 1a. GHS-R are concentrated in the hypothalamus-pituitary unit but are also distributed in other central and peripheral tissues. Apart from the potent GH-releasing action, ghrelin has other actions including stimulation of lactotroph and corticotroph function, influence on the pituitary gonadal axis, stimulation of appetite, control of energy balance, influence on sleep and behavior, control of gastric motility and acid secretion, influence on exocrine and endocrine pancreatic function as well as on glucose metabolism, cardiovascular actions and modulation of proliferation of neoplastic cells, as well as of the immune system. The discovery of ghrelin opened many new perspectives of research in neuroendocrinology and metabolism, and even also in other fields of internal medicine as gastroenterology, immunology, oncology and cardiology. The possibility that ghrelin and/or GHS analogs, acting as either agonists or antagonists on different activities, might have clinical impact is obviously suggested and is receiving great attention.