Hormones: Prostaglandins

The prostaglandins are a group of lipids made at sites of tissue damage or infection that are involved in dealing with injury and illness. They control processes such as inflammation, blood flow, the formation of blood clots and the induction of labour.

Mechanism of aspirin action.

Mechanism of action of the drug aspirin. Aspirin works by preventing the production of prostaglandin: aspirin molecules (blue hexagons) enter the cell and chemically modify the cyclooxygenase enzyme (purple) to prevent prostaglandin synthesis.

Alternative names for prostaglandins

Prostaglandin D2; prostaglandin E2; prostaglandin F2; prostaglandin I2 (which is also known as prostacyclin); a closely related lipid called thromboxane.

What are prostaglandins?

Unlike most hormones, the prostaglandins are not secreted from a gland to be carried in the bloodstream and work on specific areas around the body. Instead, they are made by a chemical reaction at the site where they are needed and can be made in nearly all the organs in the body. Prostaglandins are part of the body’s way of dealing with injury and illness.

The prostaglandins act as signals to control several different processes depending on the part of the body in which they are made. Prostaglandins are made at sites of tissue damage or infection, where they cause inflammation, pain and fever as part of the healing process. When a blood vessel is injured, a prostaglandin called thromboxane stimulates the formation of a blood clot to try to heal the damage; it also causes the muscle in the blood vessel wall to contract (causing the blood vessel to narrow) to try to prevent blood loss. Another prostaglandin called prostacyclin has the opposite effect to thromboxane, reducing blood clotting and removing any clots that are no longer needed; it also causes the muscle in the blood vessel wall to relax, so that the vessel dilates. The opposing effects that thromboxane and prostacyclin have on the width of blood vessels can control the amount of blood flow and regulate response to injury and inflammation.

Prostaglandins are also involved in regulating the contraction and relaxation of the muscles in the gut and the airways.

Prostaglandins are known to regulate the female reproductive system, and are involved in the control of ovulation, the menstrual cycle and the induction of labour. Indeed, manufactured forms of prostaglandins - prostaglandin E2 and F2 can be used to induce (kick-start) labour.

How are prostaglandins controlled?  

The chemical reaction that makes the prostaglandins involves several steps; the first step is carried out by an enzyme called cyclooxygenase. There are two main types of this enzyme: cyclooxygenase-1 and cyclooxygenase-2. When the body is functioning normally, baseline levels of prostaglandins are produced by the action of cyclooxygenase-1. When the body is injured (or inflammation occurs in any area of the body), cyclooxygenase-2 is activated and produces extra prostaglandins, which helps the body to respond to the injury.

Prostaglandins carry out their actions by acting on specific receptors; at least eight different prostaglandin receptors have been discovered. The presence of these receptors in different organs throughout the body allows the different actions of each prostaglandin to be carried out, depending on which receptor they interact with.

Prostaglandins are very short-lived and are broken down quickly by the body. They only carry out their actions in the immediate vicinity of where they are produced; this helps to regulate and limit their actions.

What happens if I have too much prostaglandins?

High levels of prostaglandins are produced in response to injury or infection and cause inflammation, which is associated with the symptoms of redness, swelling, pain and fever.  This is an important part of the body’s normal healing process.

However, this natural response can sometimes lead to excess and chronic production of prostaglandins, which may contribute to several diseases by causing unwanted inflammation. This means that drugs, which specifically block cyclooxygenase-2, can be used to treat conditions such as arthritis, heavy menstrual bleeding and painful menstrual cramps and certain types of cancer including colon and breast cancer. New discoveries are being made about cyclooxygenases which suggest that cyclooxygenase-2 is not just responsible for disease but has other functions.

Anti-inflammatory drugs, such as aspirin and ibuprofen, work by blocking the action of the cyclooxygenase enzymes and so reduce prostaglandin levels. This is how these drugs work to relieve the symptoms of inflammation. Aspirin also blocks the production of thromboxane and so can be used to prevent unwanted blood clotting in patients with heart disease.

What happens if I have too few prostaglandins?

Manufactured prostaglandins can be used to increase prostaglandin levels in the body under certain circumstances. For example, administration of prostaglandins can induce labour at the end of pregnancy or abortion in the case of an unwanted pregnancy. They can also be used to treat stomach ulcers, glaucoma and congenital heart disease in newborn babies. Further advances in understanding how prostaglandins work may lead to newer treatments for a number of conditions.

Mechanism of action of the drug aspirin. Aspirin works by preventing the production of prostaglandin: aspirin molecules (blue hexagons) enter the cell and chemically modify the cyclooxygenase enzyme (purple) to prevent prostaglandin synthesis.