Prostaglandins, together with thromboxanes (collectively termed prostanoids), are fatty acid derivatives of significant importance in many physiological processes. These compounds are formed following the action of cyclooxygenases (COX) and associated enzymes on C20 polyunsaturated fatty acid precursors released from phospholipids in membranes. Nearly all mammalian cell types have the biosynthetic machinery to produce at least one type of prostanoid. The same C20 fatty acid substrates can also

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... e acted upon by lipoxygenases to produce mono-di-and trihydroxy derivatives such as leukotrienes, lipoxins and resolvins. The final route is the cytochrome P 450 pathway that can convert C20 fatty acids to hydroxylated derivatives. Collectively these compounds are called eicosanoids; the term derived from the Greek eikosi that refers to the C20 backbone in the parent fatty acid. Prostaglandins (PGs) were first discovered in the 1930s by von Euler and colleagues, who found a substance produced by the prostate gland that caused smooth muscle contraction. They christened the active substance 'prostaglandin', but it was over 30 years until the structure and mode of biosynthesis of these fatty acid derivatives became fully understood. PGs have many basic physiological functions where they act as 'local' hormones. For example, thromboxane (Tx) A 2 and prostacyclin (PGI 2 ) generated by platelets and endothelial cells, respectively, regulate the aggregatory behaviour of 3