How do prostaglandins and Leukotrienes promote inflammation?
PGs (especially PGD 2 ) induce local vasodilation and increased vascular permeability. PGE 2 is the most abundant PG at inflammation sites and can have both proinflammatory and antiinflammatory effects depending on the receptor it activates. LTs fall into two classes: (1) LTC 4 , LTD 4 , and LTE 4 induce smooth muscle contraction, bronchoconstriction, and mucous secretion. They were once collectively called slow-reacting substance of anaphylaxis or SRS-A; (2) LTB 4 has none of the above properties but is a potent chemotactic factor for neutrophils.
Note that as the inflammatory process progresses, the same COX and LOX enzymes that initially produced PGs and LTs will shift to producing specialized proresolving mediators (SPMs) that dampen the inflammatory response. These SPMs include lipoxins enzymatically derived from arachidonic acid and resolvins and protectins from omega-3 PUFFA. Notably, omega-3 PUFFA from exogenous dietary sources can serve as substrates for COX and LOX resulting in the production of resolvins and protectins, which are antiinflammatory.