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Hormone Hoopla: Movers and Shakers of Diabetes (Part 2)
April 16, 2012
Hormones are chemical messengers in the body, produced by the endocrine glands. The glands of the endocrine system, including the pancreas, produce hormones that travel throughout the bloodstream or throughout the lymph system to reach their designated targets.
The hypothalamus, which is located in the brain, is the mastermind behind all of these endocrine activities. Hormone secretion is tightly regulated by both the endocrine and the nervous systems to maintain balance, or what is known as “homeostasis.” Of course, nothing is perfect, and the balance of hormones can get off kilter, causing unwanted results. For example, if too much growth hormone is secreted during childhood, a condition called gigantism results. If too little growth hormone is secreted, the opposite condition occurs, called pituitary dwarfism.
Who do you call when you have an endocrine problem? No, not Ghostbusters, but rather, an endocrinologist. An endocrinologist is a physician who specializes in conditions of — you guessed it — the endocrine system. Many of you probably see an endocrinologist for your diabetes, but you may also have an endocrinologist if you have a thyroid disorder, a bone disorder (like osteoporosis), or Cushing syndrome (a condition resulting from too much cortisol). Of course, not everyone needs to see an endocrinologist, but these doctors are available if needed.
More Diabetes-Related Hormones
Incretins. Incretins are hormones that increase insulin secretion. There are two main types of incretins — GLP-1 and GIP.
GLP-1 is an acronym for “glucagon-like peptide-1.” This hormone is released from endocrine cells in the small intestine, or gut, during digestion. Glucose is the trigger that causes GLP-1 to be released. GLP-1 then travels through the blood to the beta cells in the pancreas where it signals them to release insulin. GLP-1 won’t be released, however, unless there is sufficient glucose around, so it’s really only released when you eat a meal that contains a fair amount of carbohydrate. GLP-1 also slows stomach emptying and blocks glucagon secretion.
In the case of Type 2 diabetes, there may be insufficient GLP-1 secreted, meaning that the beta cells are not being adequately signaled to release more insulin. We now have medicines available, called “incretin mimetics,” to address this issue. As the name implies, these drugs “mimic” GLP-1. Byetta (exenatide), Bydureon (exenatide-extended release), and Victoza (liraglutide) are the three available incretin mimetics. These are taken by injection in a manner similar to insulin, and they are approved only for people with Type 2 diabetes.
On a side note, GLP-1 is broken down very quickly in the body, thanks to an enzyme called DPP-4. The breakdown means that less insulin is secreted. A class of drugs, called DPP-4 inhibitors, literally inhibits the enzyme, helping GLP-1 do its job. Some of you may be taking these drugs, which are Januvia (sitagliptin), Onglyza (saxagliptin), and the newer one, Tradjenta (linagliptin). These are not the same as incretin mimetics, however.
GIP, which is short for “gastric inhibitory peptide,” is also secreted from the small intestine in response to glucose and fat, and helps stimulate the release of insulin from the beta cells.
Leptin. The word “leptin” comes from the Greek word “leptos,” which means thin. This hormone was discovered in 1994 and it generated a lot of excitement at the time, as researchers believed this could be the answer to overweight and obesity.
Unfortunately, that has not proved to be the case. Leptin is secreted by fat cells and it travels to the brain, telling it that your body has enough energy and can function as it should. When one diets in an effort to lose weight, less leptin is made. The brain then thinks that the body may be in starvation mode and makes an effort to boost leptin levels back up. The result? You start to eat more.
Overweight people tend to have large amounts of leptin in the body. Thanks to leptin resistance (similar to insulin resistance in Type 2 diabetes), though, leptin levels keep increasing, but the brain doesn’t sense this. These folks keep feeling hungry, keep eating, and keep gaining weight.
Giving leptin to someone who has leptin resistance doesn’t help him lose weight, so disappointingly, it’s not an effective weight-loss treatment. And leptin supplements that you might come across on the Internet don’t even contain leptin. However, leptin may prove useful for other things, like promoting bone and heart health, as well as fertility.
Ghrelin. Ghrelin is a hormone made in the stomach that tells the brain that it’s time to eat. Levels of ghrelin increase before a meal, and then drop once a person has eaten. It’s thought to work opposite leptin, which tends to cause feelings of fullness (in the absence of leptin resistance, that is).
Research shows that when ghrelin levels are high, people tend to go for high-calorie foods as opposed to, say, a salad. And giving ghrelin to someone will cause him to eat more (which could be promising for those who are trying to gain weight).
In the future, we may see medicines that block the action of ghrelin. Until then, you may be able to keep your ghrelin levels in check (helping you eat less, in other words) by making sure to include protein at each meal.
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