Abstract
Ghrelin is a peptidic hormone composed of 28 aminoacid residues. It is produced by enteroendocrine cells of stomach and intestine.
It is also produced in pancreas, kidney, placental tissue, thyroid gland, hypothalamus, and hypophysis. Gastrectomy leads to 65-80% decrease of plasma levels of ghrelin.
In human organism, ghrelin stimulates secretion of growth hormone, prolactin, and ACTH. Ghrelin also has orexigenic activity (increases food intake), influences the sleep/wake cycle, gastric motility and secretion, cardiovascular functions, regulates endocrine function of pancreas and metabolism of glucose and shows an antiproliferative effect.
Ghrelin is an important regulatory part of the homeostasis of the organism, and iterconnects neuroendocrine and metabolic response of the organism to starvation, and it is considered as a counterpart to leptin. Ghrelin was discovered by Japanese scientists in 1999 as a natural ligand of an "orphan" receptor GHS1a, which is specific for a group of synthetic peptides (growth hormone secretagogues--GHS) stimulating secretion of growth hormone.
Plasma levels of ghrelin reflect short-time changes of food intake, as well as long-time changes of the nutritional state of the organism. Plasma levels of ghrelin are decreased after food intake and in obese humans, and they are increased during starvation and in patients with mental anorexia.
Plasma levels of ghrelin in humans correlate negatively with body mass index, amount of body fat, size of adipocytes, and plasma levels of insulin, glucose, and leptin. Thus, ghrelin probably plays a role as a metabolic signal of hunger.