Figure 1.

Niacin activates the arachidonic acid cascade to induce vasodilatation. Niacin activates the G-protein coupled receptor 109A (GPR109A) to increase cAMP and releases arachidonic acid from cell membranes. Arachidonic acid is metabolised to produce prostaglandins, prostacyclin and thromboxane. Activation of the prostaglandin D₂ receptor (DP₁), prostaglandin E₂ receptor (EP₂), EP4 and IP receptors can lead to vasodilatation that may contribute to flushing. NSAIDs block the metabolism of arachidonic acid, while LRP blocks DP₁-mediated vasodilatation. cAMP, cyclic AMP; PLA2, phospholipase A2; PG, Prostaglandin; CRTH2, chemoattractant receptor homologous-molecule expressed on T helper type 2; NA, nicotinic acid; NSAIDs, non-steroidal anti-inflammatory drugs; LRP, laropiprant