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Physiology of ghrelin and related peptides
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
This review article discusses the physiology of ghrelin and related peptides in growth hormone (GH) regulation. The authors describe GH release under hypothalamic GHRH and somatostatin control, recount Cyril Bowers' discovery of GH-releasing peptide (GHRP-6) and the subsequent search for GH secretagogues and their receptor, and note that GHRH and secretagogues act through distinct G-protein-coupled receptors, secretagogues raising intracellular calcium and GHRH raising cAMP. They summarize ghrelin's characterization as the natural GHS-receptor ligand and its roles in feeding, nutritional homeostasis, and gut motility, along with other peptide modulators of GH secretion, and describe imaging of GH-release mechanisms in porcine somatotrophs.
Abstract
Growth hormone (GH) released from pituitary under direct control of hypothalamic releasing (i.e., GHRH) and inhibiting (i.e., sst or SRIF) hormones is an anabolic hormone that regulates metabolism of proteins, fats, sugars and minerals in mammals. Cyril Bowers' discovery of GH-releasing peptide (GHRP-6) was followed by a search for synthetic peptide and nonpeptide GH-secretagogues (GHSs) that stimulate GH release, as well as a receptor(s) unique from GHRH receptor. GHRH and GHSs operate through distinct G protein-coupled receptors to release GH. Signal transduction pathways activated by GHS increase intracellular Ca2+ concentration in somatotrophs, whereas GHRH increases cAMP. Isolation and characterization of ghrelin, the natural ligand for GHS receptor, has opened a new era of understanding to physiology of anabolism, feeding behavior, and nutritional homeostasis for GH secretion and gastrointestinal motility through gut-brain interactions. Other peptide hormones (i.e., motilin, TRH, PACAP, GnRH, leptin, FMRF amide, galanin, NPY, NPW) from gut, brain and other tissues also play a role in modulating GH secretion in livestock and lower vertebrate species. Physiological processes, such as neurotransmission, and secretion of hormones or enzymes, require fusion of secretory vesicles at the cell plasma membrane and expulsion of vesicular contents. This process for GH release from porcine somatotrophs was revealed by atomic force microscopy (AFM), transmission electron microscopy (TEM) and immunohistochemical distribution of the cells in pituitary during stages of development.
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