Ghrelin: central and peripheral effects of a novel peptydil hormone.

Ghrelin is a peptydil hormone that has recently been discovered through an unusual reverse pharmacology pathway. Ghrelin is produced mainly in the stomach, but its expression has also been demonstrated in many other organs such as pituitary, hypothalamus, bowel, kidney, heart, pancreas, testis. It is active on the central nervous system, where it is involved in the regulation of GH secretion, mainly through a GHRH-independent mechanism and directly at the pituitary level. Furthermore, ghrelin controls energy balance, enhancing fat mass deposition and food intake through the activation of the hypothalamic nuclei and the promotion of NPY (neuropeptide Y) and AGRP (Agouti related protein) expression; since it stimulates weight gain, ghrelin is considered a possible important factor in the etiology of obesity. Besides these main actions, ghrelin is active in the cardiovascular, reproductive and endocrine systems, and displays antineoplastic activity. Even though most studies have been conducted in humans and rats, there is increasing interest in the role of ghrelin in domestic species. We have integrated the first studies on ghrelin action with recent data on its involvement in modulating several central and peripheral activities.