Two phospholipase pools for prostaglandin synthesis in macrophages

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Abstract
Macrophages in culture produce prostaglandins [PG] in response to a variety of phagocytic and non-phagocytic stimuli. As prostaglandins are not stored in cells, and mammalian cells contain very little free arachidonic acid, synthesis and release of PG depends on the release of the precursor, arachidonic acid, from cell lipids. Many agents that stimulate cell PG production act by releasing arachidonic acid, presumably by activating phospholipase A2 or phospholipase C, depending on the cell system used. Rabbit alveolar macrophages secrete arachidonic acid and PG in response to phagocytic stimuli. This secretion depends not on particle attachment, but rather on interiorization of the particles. The time course of PG arachidonic acid secretion does not parallel that of particle engulfment per se, but of the release of lysosomal enzymes, indicating that the release of arachidonate and PG is associated with the latter. Apparently there are 2 independent pools of phospholipases in macrophages, 1 in the lysosomes and 1 elsewhere.