Abstract
Ghrelin is a relatively novel multifaceted hormone that has been found to exert a plethora of physiological effects. In this review, we found/confirmed that ghrelin has effect on all body systems. It induces appetite; promotes the use of carbohydrates as a source of fuel while sparing fat; inhibits lipid oxidation and promotes lipogenesis; stimulates the gastric acid secretion and motility; improves cardiac performance; decreases blood pressure; and protects the kidneys, heart, and brain. Ghrelin is important for learning, memory, cognition, reward, sleep, taste sensation, olfaction, and sniffing. It has sympatholytic, analgesic, antimicrobial, antifibrotic, and osteogenic effects. Moreover, ghrelin makes the skeletal muscle more excitable and stimulates its regeneration following injury; delays puberty; promotes fetal lung development; decreases thyroid hormone and testosterone; stimulates release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin; inhibits insulin release; and promotes wound healing. Ghrelin protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. Having a clear understanding of the ghrelin effect in each system has therapeutic implications. Future studies are necessary to elucidate the molecular mechanisms of ghrelin actions as well as its application as a GHSR agonist to treat most common diseases in each system without any paradoxical outcomes on the other systems.
Highlights
Ghrelin, a unique 28-amino-acid peptide, is the first identified circulating hunger hormone
Ghrelin has two forms: acyl ghrelin and des-acyl ghrelin. e octanoylation of ghrelin is critical for its physiological functions which depend upon ghrelin O-acyltransferase (GOAT)
To avoid missing studies in the search strategy, we considered different terms and names. e search strategy with the PubMed database was (“ghrelin” OR “acyl ghrelin” OR “des-acyl ghrelin” OR “growth hormone secretagogue” OR “motilin-related peptide”) AND (“physiological effect” OR “role” OR “action”)
Summary
A unique 28-amino-acid peptide, is the first identified circulating hunger hormone. It is a hormone in the endocrine system and a neurotransmitter in the nervous system. Des-acyl ghrelin is a nonoctanoylated and inactive form that does not activate the growth hormone secretagogue receptor, which is a target for acyl form to release growth hormone (GH). Knockout of mTOR in X/A-like cells increases circulating acyl ghrelin. Long-chain fatty acids, insulin, glucagon, GH inhibitory hormone, oxytocin, and dopamine (DA) regulate ghrelin release by directly acting on ghrelinproducing cells [30, 42,43,44]. Plasma acyl ghrelin concentration is increased by the α-adrenergic antagonists and β-adrenergic agonists that act directly on β1 receptors in ghrelin-secreting cells [30]. It is important for preparing ghrelin agonists and antagonists
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