What is Glucagon – Like Peptides (GLP-1)?

By Dr Harold Gunatillake Health Writer

A-cells of the Islet of Langerhans in the pancreas produce Glucagon whilst Beta-cells of the Islet secrete insulin. Glucagon has a major role in maintaining normal glucose concentration in blood and has the opposite effect of insulin.

Insulin reduces the blood glucose level through a 'courier mechanism'. The excess glucose in the blood from digested carbs (rice, flour products, vegetables, etc.) is taken to the liver and fat cells for storing, thus maintaining a normal glucose level in the blood, in non-diabetics (normo-glycaemia).

Diabetics do not secrete sufficient insulin in the beta cells of the pancreas due to a stressed pancreas or worn-out exhausted islet cells and result in rise of glucose level in the blood (hyperglycemia). Diabetic subjects need to take tablets that boost the production of insulin or with further wearing of beta cells with time, they may need to start on insulin therapy.

Glucagon is also produced in the L cells of the intestinal mucosa and also in certain neurons (extensions of nerve cells) of the brain and spinal cord (central nervous system), mainly in the hypothalamus.

It functions as a counter-regulatory hormone that opposes the action of insulin and maintains the levels of blood glucose at normal levels, especially when the glucose level drops, in normal and diabetic patients (hypoglycemia). In other words this hormone (glucagon) increases the blood glucose level and insulin hormone reduces the blood glucose level.

The brain in particular depends on glucose as a fuel for energy and glucagon manufacture becomes an important mechanism for survival in situations of starvation.

The liver has a special mechanism to control sugar level when it drops below normal range. Glucagon stimulates breakdown of glycogen stored in the liver at times of emergencies. When blood sugar levels are high, large amounts of glucose are taken up by the liver with the assistance of insulin, and is stored as glycogen. Later, when blood glucose levels begin to fall, glucagon is secreted and acts on liver cells (hepatocytes) to activate the enzyme that depolarize glycogen and release glucose.

Glucagon also appears to have a minor effect of enhancing lipolysis (breakdown of fat) from the stored triglyceride in the fat cells (adipose tissue). This way the glucose is preserved and fatty acid from the breakdown of fats provide fuel for most body cells.

Protein conversion to glucose
After consumption of large quantity of protein rich meat, which is broken down into amino-acid through the digestive process, then, glucogen participates in the conversion of excess amino-acids to glucose by enhancing gluconeogenesis (new glucose synthesis) in the liver. High levels of amino acids in the blood also stimulate insulin release helping to reduce glucose level in the blood.

This paragraph is a bit confusing and you may need to read a few times to understand the mechanisms.

Lost in the jungle
Say, you get lost in the jungle. You have no food. The glucose level in the blood will come down because the body, including the brain and muscles utilize the blood glucose for their metabolic needs (state of hypoglycaemia). In such a situation the pancreas and the gut secretes Glucagon –like peptide (GPL-1) to release the stored glucose from the fat cells and the liver (stored as glycogen)into the blood stream to bring about glucose homeostasis through this enhanced mobilization of glucose.

That is the reason you could survive in the jungle for many days without food but not water. Among diabetics also glucagon mechanism works. Say your fasting glucose level in the morning is 5.5m.mol/dl. Even without having breakfast and not taking anti-diabetic medication the glucose level will commonly rise to say 7 m.mol/dl. You get confused and frustrated thinking how the sugar level in the blood rose even without having breakfast. Invariably you would ring your diabetic specialist and ask for an explanation.

Your specialist will laugh and say, "Don't worry; there is a natural mechanism to increase your glucose level when it goes too low. Glucagon hormone (GPL-1) does it". You would be most relieved with that explanation.

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