Ghrelin the hunger hormone By: Katie McMahon

What is Ghrelin Ghrelin is a 28 amino acid peptide and hormone that is produced mainly by P/D1 cells lining the fundus of the human stomach and epsilon cells of the pancreas that stimulates hunger. Ghrelin levels increase before meals and decrease after meals. It is considered the counterpart of the hormone leptin, produced by adipose tissue, which causes fullness when present at higher levels.

Discovery of Ghrelin The discovery of ghrelin followed after the discovery of the ghrelin receptor in 1996 and was reported by Masayasu Kojima and colleagues in The name is based on its role as a growth hormone-releasing peptide with reference to the Proto-Indo-European root ghre, meaning to grow.

When Ghrelin levels are high When ghrelin levels are too high, the brain wants food even if we are full and the food we crave is high in calories and loaded with fat. Ghrelin actually helps you feel good. In fact it helps you feel REALLY GOOD by activating some of the same regions of brain that are also activated by cocaine!

Studies on Ghrelin In a study on mice, Dr. Jeffrey Zigman and his team found that mice injected with ghrelin chose to be in a room previously anchored with a high calorie treat versus a room anchored with a low calorie treat. The mice not injected with ghrelin had no preference for either room. In a second test, Zigman tested how long mice would continue to poke their noses into a hole in order to receive a pellet of high- fat food. The non-ghrelin group gave up far faster than the mice injected with ghrelin.

Ghrelin’s actions Ghrelin has many actions, but the most prominent one is that it increases hunger by stimulating neurons in the nucleus of the hypothalamus, especially the neurons that express neuropeptide Y and agouti-related protein. Neuropeptide Y and agouti-related protein are both strong stimulators of appetite. Not only that, neuropeptide Y and agouti-related protein also enhance appetite by reducing the action of the appetite inhibitors. This is why people who are given injections of ghrelin become extremely hungry and eat more than they otherwise would.

Ghrelin and anti-obesity strategy attempts Because of ghrelin's role in enhancing hunger, it is a prominent target of anti-obesity strategies. However, counteracting ghrelin has proved to be harder than expected. Although hunger control doesn’t look promising knowing more about this hormone will still help us. When the clock is moving toward lunch or dinner-time and we find ourselves obsessing about food, its good to know that we aren’t actually starving, we are simply getting a signal from our stomachs that is time to start foraging for food.

Ghrelin does have a specific role in the energy management of the body. Researchers at Columbia and Rockefeller Universities have shown that ghrelin is released in a circadian manner, prior to the onset of mealtimes. This pattern is illustrated in the graph below

Causes of high Ghrelin levels Lack of sleep Low thyroid function Eating disorders such as anorexia and bulimia

Ghrelin’s counter Hormone: Leptin Leptin tells your brain that you have enough energy stored in your fat cells to engage in normal, relatively expensive metabolic processes," he says. "In other words, when leptin levels are at a certain threshold -- for each person, it's probably genetically set -- when your leptin level is above that threshold, your brain senses that you have energy sufficiency, which means you can burn energy at a normal rate, eat food at a normal amount, engage in exercise at a normal rate, and you can engage in expensive processes, like puberty and pregnancy". But when people diet, they eat less and their fat cells lose some fat, which then decreases the amount of leptin produced.

When Ghrelin Spikes or Falls Ghrelin levels are mainly regulated by nutritional and metabolic factors; in fact they are increased by energy restriction (such as malnutrition or anorexia) and decreased by food intake and overfeeding. Several studies showed reduced ghrelin levels in patients with obesity and ghrelin levels increase in obese subjects when they lose weight

The End