The biochemistry of prostaglandins: a primer

The membranes of cells serve to endow structural integrity, compartmentalize regions of the cell and allow the generation of a stable intracellular milieu. The lipid component of the membrane forms a matrix for structurally and functionally important proteins. It is also increasingly obvious that these lipids form substrates for the synthesis of a range of molecules which have a central role in cellular communication and regulation. The prostaglandins were the first class of such molecules described and to some extent may serve as an archetype for an understanding of the various classes of lipid mediators. The release of arachidonic acid from lipids (phospholipids in particular) is achieved by lipases (phospholipase A2). Arachidonic acid itself may act directly on cells to modify function. For instance, it may modulate ion channel function. However, it is more often a substrate for cyclooxygenase which produces prostaglandin H2, being the precursor for further prostaglandin and thromboxane synthesis, or for lipoxygenase, to produce the precursor for leukotrienes (a related class of mediators). The prostaglandins may act intracellularly, are readily released from cells to act in an autocrine or paracrine fashion, and may enter the blood vessels or lymphatics to exert endocrine effects. Target cells may contain receptors with relative specificity for various members of the prostaglandin family, thus eliciting some specificity of action by the mediators.