Ghrelin: A 28-amino acid, acylated, orexigenic peptide that is a ligand for GROWTH HORMONE SECRETAGOGUE RECEPTORS. Ghrelin is widely expressed but primarily in the stomach in the adults. Ghrelin acts centrally to stimulate growth hormone secretion and food intake, and peripherally to regulate energy homeostasis. Its large precursor protein, known as appetite-regulating hormone or motilin-related peptide, contains ghrelin and obestatin.Receptors, Ghrelin: Transmembrane proteins that recognize and bind GHRELIN, a potent stimulator of GROWTH HORMONE secretion and food intake in mammals. Ghrelin receptors are found in the pituitary and HYPOTHALAMUS. They belong to the family of G-PROTEIN-COUPLED RECEPTORS.Peptide Hormones: Hormones synthesized from amino acids. They are distinguished from INTERCELLULAR SIGNALING PEPTIDES AND PROTEINS in that their actions are systemic.Appetite: Natural recurring desire for food. Alterations may be induced by APPETITE DEPRESSANTS or APPETITE STIMULANTS.Eating: The consumption of edible substances.Leptin: A 16-kDa peptide hormone secreted from WHITE ADIPOCYTES. Leptin serves as a feedback signal from fat cells to the CENTRAL NERVOUS SYSTEM in regulation of food intake, energy balance, and fat storage.Peptide YY: A 36-amino acid peptide produced by the L cells of the distal small intestine and colon. Peptide YY inhibits gastric and pancreatic secretion.Stomach: An organ of digestion situated in the left upper quadrant of the abdomen between the termination of the ESOPHAGUS and the beginning of the DUODENUM.Appetite Stimulants: Agents that are used to stimulate appetite. These drugs are frequently used to treat anorexia associated with cancer and AIDS.Human Growth Hormone: A 191-amino acid polypeptide hormone secreted by the human adenohypophysis (PITUITARY GLAND, ANTERIOR), also known as GH or somatotropin. Synthetic growth hormone, termed somatropin, has replaced the natural form in therapeutic usage such as treatment of dwarfism in children with growth hormone deficiency.Growth Hormone: A polypeptide that is secreted by the adenohypophysis (PITUITARY GLAND, ANTERIOR). Growth hormone, also known as somatotropin, stimulates mitosis, cell differentiation and cell growth. Species-specific growth hormones have been synthesized.Appetite Regulation: Physiologic mechanisms which regulate or control the appetite and food intake.Fasting: Abstaining from all food.Acylation: The addition of an organic acid radical into a molecule.Hunger: The desire for FOOD generated by a sensation arising from the lack of food in the STOMACH.Gastric Emptying: The evacuation of food from the stomach into the duodenum.Postprandial Period: The time frame after a meal or FOOD INTAKE.Receptors, G-Protein-Coupled: The largest family of cell surface receptors involved in SIGNAL TRANSDUCTION. They share a common structure and signal through HETEROTRIMERIC G-PROTEINS.Insulin: A 51-amino acid pancreatic hormone that plays a major role in the regulation of glucose metabolism, directly by suppressing endogenous glucose production (GLYCOGENOLYSIS; GLUCONEOGENESIS) and indirectly by suppressing GLUCAGON secretion and LIPOLYSIS. Native insulin is a globular protein comprised of a zinc-coordinated hexamer. Each insulin monomer containing two chains, A (21 residues) and B (30 residues), linked by two disulfide bonds. Insulin is used as a drug to control insulin-dependent diabetes mellitus (DIABETES MELLITUS, TYPE 1).Growth Hormone-Releasing Hormone: A peptide of 44 amino acids in most species that stimulates the release and synthesis of GROWTH HORMONE. GHRF (or GRF) is synthesized by neurons in the ARCUATE NUCLEUS of the HYPOTHALAMUS. After being released into the pituitary portal circulation, GHRF stimulates GH release by the SOMATOTROPHS in the PITUITARY GLAND.Feeding Behavior: Behavioral responses or sequences associated with eating including modes of feeding, rhythmic patterns of eating, and time intervals.Neuropeptide Y: A 36-amino acid peptide present in many organs and in many sympathetic noradrenergic neurons. It has vasoconstrictor and natriuretic activity and regulates local blood flow, glandular secretion, and smooth muscle activity. The peptide also stimulates feeding and drinking behavior and influences secretion of pituitary hormones.Satiety Response: Behavioral response associated with the achieving of gratification.