The role of ghrelins Essay Example for Free

The role of ghrelins Essay Ghrelin is a general name for a class of hormones found in the gastrointestinal tract of vertebrates. It is a preprohormone containing a chain of 28 amino acid peptides. During synthesis, a modification arises whereas n-octanoic acid is bound to one of its amino acids. This makes it capable of playing its biological role. Ghrelins are synthesized at the fundus lining the stomach. It is primarily produced by epithelial cells lining the fundus. However, smaller amounts have also been detected in the kidneys, placenta, hypothalamus and the pituitary gland. (Brown, 2006) The ghrelin receptor was known before the discovery of ghrelin. It is located in the anterior pituitary and stimulates secretion of growth hormone when activated. It was named GHS-R or growth hormone secretagoue receptor. In 1999, Kojima et al. announced that they have discovered the natural ligand for GHS-R.   They named it ghrelin, deriving it form the word â€Å"ghre† which means grow in Proto-Indo-European languages. They obtained it from rat stomach and investigated its role in pituitary growth hormone and energy homeostasis functions. (Kojima Kangawa, 2004) Roles of ghrelin Ghrelin is the ligand of GHS-r. Its signal together with that of semostatin and other growth hormone inducers control the timing as well as the magnitude of growth hormone excretion. It is suggested that the stomach releases ghrelin into the bloodstream, where it is conveyed to the potiuitary gland, triggering the release of growth hormone. Kanagawa et al. found significant amounts of ghrelin in healthy people.(Kojima et al., 1999) In 2000, Ezio Ghigo et al. discovered that ghrelin injections led to prolonged increase of growth hormone concentrations in the blood. (Dickson, 1999)   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   Ghrelin   also seems to stimulate appetite. Lab tests in rats show ann increase in body weight after ghrelin injections. This effect is independent of ghrelin’s role in GH stimulation. In people, a popular side effect of taking ghrelin containing drugs was the sensation of intense hunger. About 80% of test participants in a study to test ghrelins growth hormone functions also suffered an increase of appetite. It was found that ghrelin concentration in the blood increases as a person grows hungry and decreases as that person’s hunger is sated.   Another study showed that people injected with ghrelin before meals increased their food intake by 30%. (Cummings et al., 2002) Another study also showed that resting   ghrelin levels rise as net body weight decreases and returns once a set point is reached. This means that the body regulates ghrelin levels based on a specific body weight attainment, making you hungrier as you lose more weight. Persons with anorexia nervosa, a disorder in which people starve themselves show extremely high amounts of ghrelin. But it seems in their cases, their body does not listen. (Travis, 2002)The increase of ghrelins is also related to time as discovered by Yildiz et al. An increase in ghrelin was noted between midnight to dawn, mhowever, hunger is suppressed by other hormones, making it easier to fall asleep and eat in the morning after.(Yildiz, Suchard, Wong, McCann, Licinio, 2004)Alos, lack of sleep particularly in obese persons lead to production of ghrelin and less production of leptin, the hormone which suppresses appetite. Ghrelin levels also decrease dramatically with the conduction of gastric bypass surgery. Animal research has also discovered that ghrelin may enhance memory and learning as it enters the hippocampus via the bloodstream. High ghrelin levels, particularly before meals when the stomach is empty may be the time most conducive to learning. (Philips, 2006) REFERENCES Brown, R. (2006). Ghrelin.  Ã‚   Retrieved March 11, 2007, from http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/ghrelin.html Cummings, D., Weigle, D., Frayo, R., Breen, P., Ma, M., Dellinger, E., et al. (2002). Plasma Ghrelin Levels after Diet-Induced Weight Loss or Gastric Bypass Surgery. New England Journal of Medicine(346), 1623-1630. Dickson, S. L. (1999). Ghrelin: A newly discovered hormone  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   [Electronic Version]. British Society for Neuroenterology from http://neuroendo.org.uk/index.php/content/view/26/11/. Kojima, M., Hosoda, H., Date, Y., Nakazato, M., Matsuo, H., Kangawa, K. (1999). Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature 402, 656-660 (402), 656-660. Kojima, M., Kangawa, K. (2004). Ghrelin: Structure and Function   [Electronic Version]. Physiological Review, 85, 495-522. Retrieved March 11 2007. Philips, M. L. (2006). Hunger hormone tied to learning [Electronic Version]. The Scientist. Retrieved March 11 2007 from http://www.the-scientist.com/news/display/23132/. Travis, J. (2002). The Hunger Hormone? [Electronic Version]. Science News Online, 161, 107. Retrieved March 11 2007 from http://www.sciencenews.org/articles/20020216/bob10.asp. Yildiz, B. O., Suchard, M. A., Wong, M.-L., McCann, S. M., Licinio, J. (2004). Alterations in the dynamics of circulating ghrelin, adiponectin, and leptin in human obesity [Electronic Version]. Medical Sciences. Retrieved March 11 2007 from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=478601.