PG
Meaning of PG: Short-lived local messengers built from a fatty acid, and the molecules that ordinary painkillers work by shutting down.
Definition of PG
PG is the standard abbreviation for prostaglandin, one of a family of fat-derived signaling molecules made throughout the body from a fatty acid stored in cell membranes. Prostaglandins are produced on demand, act on the tissue immediately around them, and break down within seconds to minutes. Different members raise or lower blood pressure, contract or relax smooth muscle, and drive fever, pain and inflammation.
Are they hormones?
Not in the strict sense, although the older description as hormone-like is still common. A hormone is made by a gland, released into the blood and carried to a distant target. A prostaglandin is made by almost any cell, is not stored anywhere, and is destroyed so quickly that it rarely reaches the bloodstream in a meaningful amount. Its target is the cell next door. The name itself is a historical accident: the activity was first found in semen and credited to the prostate, which turned out not to be the main source.
How are they made and blocked?
The raw material is arachidonic acid, released from the fatty layer of the cell membrane when a cell is disturbed. An enzyme called cyclooxygenase, usually shortened to COX, converts it into the parent compound from which the individual members are built. Aspirin and the other anti-inflammatory painkillers work by blocking that enzyme, which is why a single class of drug relieves pain, lowers fever and reduces swelling at once. It also explains their stomach and kidney effects, since the same molecules protect the stomach lining and help regulate blood flow through the kidney.
What do individual members do?
| Member | Main action |
|---|---|
| Prostaglandin E2 | Fever, pain sensitivity, protection of the stomach lining |
| Prostaglandin F2 alpha | Contraction of the womb and of airway muscle |
| Prostacyclin | Widens vessels and discourages clotting |
| Thromboxane | Narrows vessels and promotes clotting |
The last two come off the same pathway and pull in opposite directions, and the balance between them is part of how blood pressure and clotting are held steady. Manufactured versions serve as drugs in their own right: to start labor, to hold a vessel open in a newborn heart defect, and to lower pressure inside the eye.
Also known as
Used in a sentence
PG levels in the tissue rose sharply during the inflammatory response.
Good to know
Prostaglandins are made on demand by ordinary cells and act where they are made rather than travelling in the blood, so they are not hormones in the strict sense, and blocking their production removes protective effects in the stomach and kidney alongside the relief of pain.