|
Indian Journal of Pharmacology, Vol. 37, No. 2, March-April, 2005, pp. 133-134 Molecules of the Millennium Ghrelin: A potential drug target for obesity Madan A.K. College of Veterinary and Animals Sciences, GBPUAT, Pantnagar Code Number: ph05028 The suffix "ghre" means "to grow". Ghrelin (pronounced GRELL-in) was discovered in 1999 as a peptide hormone that potently stimulates the release of growth hormone from the anterior pituitary. It was subsequently determined that ghrelin, along with several other hormones, has significant effects on appetite and energy balance. Ghrelin is synthesized as a pre-prohormone, and then proteolytically processed to yield a 28-amino acid peptide. A modification necessary for biological activity is the binding of n-octanoic acid to one of its amino acids, carried out during its synthesis. Synthesis of ghrelin occurs predominantly in the epithelial cells lining the fundus of the stomach, with smaller amounts produced in the placenta, kidney, pituitary and hypothalamus. 1. Stimulation of growth hormone secretion: Ghrelin, as the ligand for the growth hormone secretagogue receptor, potently stimulates the secretion of the growth hormone. The ghrelin signal is integrated with that of the growth hormone-releasing hormone and somatostatin to control the timing and magnitude of growth hormone secretion.[2] 2. Regulation of energy balance: In rodents and humans, ghrelin functions to increase hunger through its action on the hypothalamic feeding centers. The plasma ghrelin concentrations increase during fasting.[3] Humans injected with ghrelin reported sensations of intense hunger.[4] Ghrelin also appears to suppress fat utilization in the adipose tissue, which is somewhat paradoxical considering that the growth hormone has the opposite effect. Overall, ghrelin seems to be one of several hormonal signals that communicate the state of energy balance in the body to the brain. Other effects of ghrelin include stimulation of gastric emptying and a variety of positive effects on cardiovascular function (e.g. increased cardiac output). It is not yet clear whether the cardiovascular effects are due to a direct effect of ghrelin or an indirect effect of ghrelin′s ability to stimulate growth hormone secretion. Disease states and ghrelin Blood concentrations of ghrelin are lowest shortly after consumption of a meal, and then gradually rise during the fast and reach the peak just prior to the next meal. Ghrelin concentrations in blood are reduced in obese humans compared to lean subjects. However, whether this is the cause or effect is not well defined. Patients with anorexia nervosa have high plasma ghrelin levels whereas obese ones tend to have low levels. A rise or fall in ghrelin is not observed in patients who had gastric bypass surgery, before or after they eat. Their levels of ghrelin remain low all the time. This shows that stomach cells produce ghrelin only when food passes into the stomach. An empty stomach causes stimulation of ghrelin secretion while food in the stomach stops production of ghrelin. However, when no food enters the stomach for a long time, stomach cells stop producing ghrelin and a person stops being hungry. That is why when it is long past normal mealtime a person stops feeling hungry.[5] So drugs that can block ghrelin will be very effective to overcome obesity without much disturbance in the physiological homeostasis of our body. Intense research is going on in this regard for a breakthrough drug in obesity. REFERENCES
Copyright 2005 - Indian Journal of Pharmacology |
|