Prostaglandin Synthesis: The Process and Its Functions

Prostaglandin synthesis is a multi-step biochemical process in which your cells convert fatty acids from their own membranes into small, short-lived signaling molecules called prostaglandins. These molecules act locally, right near where they are made, to regulate everything from inflammation and pain to blood pressure, stomach lining protection, and labor contractions. The process hinges on a few key enzymes working in sequence, and understanding that sequence explains why common drugs like ibuprofen and aspirin work the way they do.

Where It All Starts: Freeing the Raw Material

Prostaglandins are built from arachidonic acid, a 20-carbon fatty acid that sits embedded in the membranes of your cells. It doesn’t float around freely waiting to be used. Instead, it’s locked into the phospholipids that make up cell membranes, and it has to be cut loose before anything else can happen. The enzyme responsible for this first step is cytosolic phospholipase A2 (cPLA2), which specifically targets arachidonic acid at a particular position on the phospholipid molecule.¹ This enzyme activates in response to calcium signals inside the cell, binding to membrane vesicles in a calcium-dependent way and selectively releasing arachidonic acid rather than other fatty acids.²

Think of cPLA2 as the gatekeeper of the entire prostaglandin pathway. When cells receive signals that something is happening—tissue injury, infection, hormonal shifts—calcium floods in, cPLA2 goes to work, and free arachidonic acid becomes available. Without that release, no prostaglandins get made. This is also why some anti-inflammatory strategies, including glucocorticoids like dexamethasone, were once thought to work primarily by blocking this step. Research has shown the picture is more complicated: dexamethasone can cut prostaglandin production in human endothelial cells roughly in half without actually stopping the release of arachidonic acid from phospholipids, suggesting other mechanisms are also at play.³

The Cyclooxygenase Step

Once arachidonic acid is free, it meets one of the most pharmacologically important enzymes in your body: cyclooxygenase, often abbreviated COX. This enzyme performs two reactions in sequence. First, it adds two oxygen molecules to arachidonic acid, producing an unstable intermediate called prostaglandin G2 (PGG2). Then it immediately reduces PGG2 to prostaglandin H2 (PGH2).⁴ PGH2 is the common precursor for all the major prostaglandins your body uses. It’s unstable and gets converted quickly into specific end products, but for one brief moment, it’s the universal starting material.

Your body has two main forms of this enzyme. COX-1 is present in most tissues all the time, producing prostaglandins that handle routine maintenance: protecting the stomach lining, supporting kidney blood flow, helping platelets clump when you get a cut. COX-2, by contrast, is mostly switched on during inflammation, injury, or in response to growth signals. Research has pointed to COX-2 inhibition as the primary mechanism behind the anti-inflammatory effects of drugs like ibuprofen and naproxen, while the side effects those drugs cause in the stomach and kidneys trace back to their simultaneous inhibition of COX-1.⁵

From PGH2 to Specific Prostaglandins

PGH2 doesn’t do much on its own. It’s quickly grabbed by a set of downstream enzymes called terminal synthases, each of which converts it into a different prostaglandin with a different function. Which prostaglandin gets made depends on which synthase is most active in the cell where PGH2 is produced. In a blood vessel wall cell that’s inflamed, for example, microsomal PGE2 synthase-1 (mPGES-1) converts PGH2 into prostaglandin E2 (PGE2), the prostaglandin most closely tied to inflammation. But that same PGH2 could instead be converted into prostacyclin (PGI2) by prostacyclin synthase, or into thromboxane A2 by thromboxane synthase. These enzymes compete for the same precursor.⁶

This competition matters clinically. In inflamed blood vessels, mPGES-1 activity ramps up and produces large amounts of PGE2, pulling PGH2 away from prostacyclin synthase. Less prostacyclin means less of a natural brake on clotting and blood vessel constriction. The balance between these products shapes whether a vessel stays open or starts forming a clot.

How Prostaglandins Signal

Unlike hormones that travel through the bloodstream to reach distant organs, prostaglandins work locally. Once produced, they’re secreted from the cell and act on nearby cells or even on the same cell that made them. PGE2, the best-studied prostaglandin, signals through four different receptors designated EP1 through EP4, each triggering different responses inside the target cell.⁷ This is part of why PGE2 can do seemingly contradictory things: in one tissue it promotes inflammation, in another it suppresses it, and the difference comes down to which EP receptor is present on the cells receiving the signal.

Prostaglandins are also broken down fast. The enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH) degrades PGE2 and keeps its effects confined to a small area and a short time window. This rapid turnover is one reason prostaglandins are sometimes described as “local hormones”—they act quickly, nearby, and then disappear.

Inflammation, Pain, and Fever

PGE2 is the prostaglandin most tightly linked to the classic signs of inflammation: redness, swelling, heat, and pain. In human vascular tissue, PGE2 increases the permeability of blood vessel walls, letting fluid and immune cells leak into damaged tissue, and it promotes cell migration and smooth muscle tone changes.⁸ At nerve endings, PGE2 sensitizes pain receptors, lowering the threshold at which they fire. This is why inflamed tissue hurts more than it normally would in response to the same pressure or temperature—the nerves haven’t changed, but PGE2 has made them more responsive.

PGE2 also drives fever. When your immune system detects an infection, PGE2 produced in the brain acts on EP3 receptors in the hypothalamus, the brain region that sets your body’s thermostat. This interaction raises the temperature set point, so your body starts generating heat—shivering, constricting surface blood vessels—until your actual temperature matches the new, higher target.⁹ Recent research shows that PGE2 also acts on EP3 receptors in a separate brain area called the parabrachial nucleus, where it adjusts the sensitivity of the temperature-sensing system itself. It dials down the neurons that detect warmth and ramps up the ones that detect cold, coordinating with the hypothalamic signal to allow fever to develop smoothly.¹⁰

The immune-shaping role of PGE2 goes well beyond fever. It enhances its own production in a positive feedback loop, becomes the dominant prostaglandin during chronic inflammation, and has complex effects on immune cells. It activates dendritic cells but limits their ability to recruit certain T cells, and it suppresses immune responses associated with killing infected or cancerous cells while promoting regulatory pathways that dampen immune activity.¹¹

The Cardiovascular Balancing Act

Two prostaglandin-family molecules sit on opposite sides of a tug-of-war in your blood vessels. Prostacyclin (PGI2), made mainly by cells lining the blood vessels, prevents platelets from clumping and relaxes vessel walls. Thromboxane A2, produced by platelets themselves, does the opposite: it promotes clotting and narrows blood vessels. Decades of cardiovascular research rest on the idea that keeping these two in balance is essential for preventing heart attacks and strokes.¹²

This balance is exactly what gets disrupted by selective COX-2 inhibitors, the class of painkillers developed in the late 1990s to spare the stomach while still reducing inflammation. Because prostacyclin production in blood vessels depends heavily on COX-2, these drugs reduce prostacyclin without touching thromboxane (which comes from COX-1 in platelets). The result is a shift toward clotting, higher blood pressure, and an elevated risk of heart attacks and strokes.¹³ Traditional NSAIDs like ibuprofen reduce both sides of the equation because they inhibit both COX-1 and COX-2, which is why their cardiovascular risk profile, while not zero, differs from that of selective COX-2 inhibitors.¹⁴

Protecting the Stomach and Supporting the Kidneys

Not all prostaglandin activity involves inflammation. In the stomach, prostaglandins perform essential housekeeping. They stimulate the secretion of bicarbonate and mucus, maintain blood flow to the stomach lining, and help protect the mucosal barrier against stomach acid.¹⁵ This is why regular use of NSAIDs, which suppress prostaglandin production across the board, can lead to stomach ulcers. The pain relief comes at the expense of the stomach’s built-in protective mechanism.

In the kidneys, prostaglandins—PGI2 and PGE2 in particular—serve as a safety net. Under normal conditions, your kidneys don’t rely heavily on prostaglandins to maintain blood flow. But when your body is under stress—dehydration, heart failure, heavy blood loss—prostaglandins step in to dilate the kidney’s blood vessels, keeping blood flowing through the organ and preserving its ability to filter waste and balance electrolytes.¹⁶ People who take NSAIDs while dehydrated or in heart failure can lose this protective mechanism and experience a sudden drop in kidney function, because the drugs block the very prostaglandins the kidneys are relying on.¹⁷

Reproduction and the Uterus

Prostaglandins are deeply involved in female reproduction. They help regulate the menstrual cycle, prepare the uterus for embryo implantation, and control whether the uterine muscle contracts or relaxes. At the end of pregnancy, prostaglandins play a central role in softening and dilating the cervix and driving the contractions of labor.¹⁸ Synthetic prostaglandin analogues like misoprostol are used clinically to induce labor, manage postpartum bleeding, and ripen the cervix before procedures. Menstrual cramps themselves are driven largely by prostaglandin-induced uterine contractions, which is why NSAIDs tend to be effective for period pain—they reduce the prostaglandin production fueling those contractions.

Lowering Eye Pressure

One of the more surprising therapeutic applications of prostaglandin research landed in ophthalmology. In the late 1980s, researchers discovered that prostaglandin F2α lowers intraocular pressure in primate eyes by increasing the flow of fluid out through a drainage route called the uveoscleral pathway. In treated eyes, this outflow was roughly two to three-and-a-half times higher than in untreated controls.¹⁹ That discovery led directly to the development of prostaglandin analogue eye drops, the most well-known being latanoprost, which became commercially available in 1996 and is now one of the most widely used glaucoma treatments worldwide.²⁰ These drops work by mimicking the natural prostaglandin’s ability to open up that drainage route, lowering eye pressure without many of the side effects associated with older glaucoma drugs.

Prostaglandins and Cancer

PGE2 has a complicated relationship with tumors. In the tumor microenvironment, PGE2 promotes cancer progression through several mechanisms: it encourages tumor cell growth, helps cancer cells resist programmed cell death, and stimulates the formation of new blood vessels to feed the growing tumor.²¹ Perhaps more significantly, PGE2 suppresses the immune system’s ability to recognize and attack cancer cells, creating a local environment where tumors can evade immune surveillance. High levels of PGE2 and overexpression of the enzymes that produce it have been found in many tumor types, and one of the main ways PGE2 is thought to drive cancer is by suppressing antitumor immunity via its EP2 and EP4 receptors.²²

This connection helps explain a long-standing observation: regular aspirin use is associated with a reduced risk of colorectal cancer. Aspirin irreversibly blocks COX enzymes, reducing PGE2 production in the gut over the long term. Clinical interest has turned toward developing drugs that target the EP2 and EP4 receptors specifically, potentially allowing doctors to block PGE2’s tumor-promoting effects without shutting down prostaglandin production everywhere else in the body.

How Aspirin and Ibuprofen Interact

Most people who take over-the-counter painkillers don’t realize that the timing of different NSAIDs relative to each other can matter. Aspirin works differently from ibuprofen: it permanently disables COX-1 in platelets, which is why low-dose aspirin is prescribed for heart protection. Ibuprofen, however, binds to the same enzyme site temporarily. Research found that when ibuprofen was taken before aspirin, it physically blocked aspirin from reaching and permanently inactivating COX-1 in platelets. Aspirin’s antiplatelet effect was essentially neutralized. This did not happen when aspirin was taken first, or when rofecoxib (a COX-2 inhibitor) or acetaminophen was taken before aspirin.²³ For anyone taking daily low-dose aspirin for cardiovascular protection who also uses ibuprofen for pain, the practical takeaway is straightforward: take the aspirin first and wait before reaching for the ibuprofen.

Omega-3 Fats and an Alternative Pathway

Arachidonic acid comes from omega-6 fatty acids in your diet, and the prostaglandins made from it (the “2-series,” like PGE2 and PGI2) tend to be strongly pro-inflammatory. But there’s an alternative precursor. Omega-3 fatty acids, particularly EPA (eicosapentaenoic acid) found in fish oil, can be processed through the same COX enzymes to produce a different set of prostaglandins known as the 3-series (like PGE3). These 3-series prostaglandins are generally less potent at promoting inflammation. Diets rich in omega-3 fatty acids reduce the concentration of 2-series prostaglandins while increasing 3-series production.²⁴ This shift in the prostaglandin profile is one proposed mechanism behind the anti-inflammatory reputation of omega-3 supplements and fish-heavy diets, though the clinical significance of this shift for specific diseases continues to be studied.

Prostaglandin Breakdown and Tissue Regeneration

The enzyme that degrades PGE2, 15-PGDH, has become unexpectedly interesting in aging research. In mice, inhibiting 15-PGDH—essentially letting PGE2 stick around longer rather than being rapidly broken down—was shown to potentiate tissue regeneration across multiple organs.²⁵ Later work found that 15-PGDH levels rise as tissues age, and that this increase is a hallmark of aged skeletal muscle. When researchers blocked 15-PGDH in old mice, muscle mass and strength improved.²⁶ The implication is striking: part of the decline in tissue repair capacity with aging may come from the body breaking down its own regenerative signals too quickly. Whether this translates into human therapies remains an open question, but it reframes prostaglandins as more than just inflammation molecules—they may be part of the body’s repair toolkit that fades with age.

Prostaglandin Synthesis in Other Species

Prostaglandin production is not a uniquely mammalian invention. The COX enzyme that drives prostaglandin synthesis appears to have ancient evolutionary roots, with evidence suggesting the common ancestor of simple marine animals and complex bilateral organisms already possessed a COX-like enzyme. COX homologs have been found in most crustaceans, many molluscs, and certain groups of corals and worms, though the gene seems to have been lost independently in several lineages including sea urchins and flatworms.²⁷

Insects present a fascinating twist. They produce prostaglandins and use them for reproduction, immunity, and fluid regulation, but they don’t use cyclooxygenase the way vertebrates do. Insect cell membranes contain very little arachidonic acid—less than 0.1% in some species—so they start from linoleic acid instead, converting it into arachidonic acid through additional steps. And rather than COX, they use a different enzyme called peroxinectin to produce PGH2.²⁸ The end products are similar, and many of the biological roles overlap with what prostaglandins do in mammals, but the biochemical route to get there diverged significantly. This kind of convergence—similar molecules doing similar jobs through different enzymatic machinery—suggests that the functions prostaglandins serve are so fundamental that evolution arrived at them through more than one path.