Tripping Lightly Down the Prostaglandin Pathways

By Mary G. Enig, PhD and Sally Fallon

The mysterious and complex family of prostaglandins constitutes one of the most intriguing discoveries in the history of modern medicine. Discovered in 1936 by von Euler, prostaglandins derive their name from the fact that they were first detected in human seminal fluid. It was not until the advent of more sophisticated instruments 40 years later that these compounds could be studied in depth. Researchers discovered that the original substance is just one of a family of compounds found in every cell of the body; in fact, prostaglandins are found throughout the animal kingdom, even in species as lowly as insects, shellfish and corals.

Prostaglandins are a subset of a larger family of substances called eicosanoids. Other subgroups include thromboxanes, leukotrienes and lipoxins. Eicosanoids are localized tissue hormones that seem to be the fundamental regulating molecules in most forms of life. They do not travel in the blood like hormones, but are created in the cells to serve as catalysts for a large number of processes including the movement of calcium and other substances into and out of cells, dilation and contraction, inhibition and promotion of clotting, regulation of secretions including digestive juices and hormones, and control of fertility, cell division and growth. The list of biological functions involving prostaglandins is limited only by our ignorance of their effects. As research continues, so will our knowledge of these fascinating substances expand and grow.

Prostaglandins are produced in the cells by the action of enzymes on essential fatty acids. There are two prostaglandin pathways, one that begins with double-unsaturated omega-6 linoleic acid and one that begins with triple-unsaturated omega-3 alpha-linolenic acid. Both pathways essentially involve elongation of the 18-carbon EFA's to the 20-carbon root used in each of the three eicosanoid types, plus further desaturation. (See accompanying diagram.) On the omega-6 pathway, the Series 1 prostaglandins are produced from a 20-carbon, triple unsaturated fatty acid called dihomo-y-linolenic acid (DGLA) that is found in liver and other organ meats. The Series 2 prostaglandins are produced from a 20-carbon quadruple unsaturated fatty acid called arachidonic acid (AA) found in butter, animal fats, especially pork, organ meats, eggs and seaweed. On the omega-3 pathway, the Series 3 prostaglandins are procuded from a 20-carbon quintuple unsaturated fatty acid called eicosapentaenoic acid (EPA) found plentifully in fish liver oils and fish eggs.

Early research focused on the interplay between the Series 1 and Series 2 prostaglandins. In the most simple terms, the Series 2 prostaglandins seem to be involved in swelling, inflammation, clotting and dilation, while those of the Series 1 group have the opposite effect. This has led some writers, notably Barry Sears in his popular book The Zone, to call the Series 2 family the "bad" eicosanoids and to warn readers against eating liver and butter, sources of arachidonic acid, the Series 2 precursor. Sears also asserts that perfect balance of the various prostaglandin series can be achieved by following a diet in which protein, carbohydrate and fat are maintained in certain strict proportions. This is a highly simplistic view of the complex interactions on the prostaglandin pathway, one which does not take into account individual requirements for macro and micro nutrients, nor of imbalances that may be caused by nutritional deficiencies, environmental stress or genetic defects. Like all systems in the body, the many eicosanoids work together in an array of loops and feedback mechanisms of infinite complexity. Furthermore, liver and eggs are both highly nutritious foods. Liver supplies DGLA, a precursor of the Series 1 prostaglandins, and both liver and eggs supply DHA, an important nutrient for the brain and nervous system. Arachadonic acid found in butter and eggs is also an important constituent of cell membranes.