Niacin-induced “Flush” Involves Release of Prostaglandin D2 from Mast Cells and Serotonin from Platelets: Evidence from Human Cells in Vitro and an Animal Model

Niacin lowers serum cholesterol, low-density lipoprotein, and triglycerides, and it raises high-density lipoprotein. However, most patients experience cutaneous warmth and vasodilation (flush). Acetylsalicylic acid (ASA) can reduce this flush, presumably by decreasing prostaglandin D2 (PGD2) release from macrophages. Here, we show that methylnicotinate induces significant PGD2 release from human mast cells and serotonin from human platelets. Intradermal injection of methylnicotinate induces rat skin vasodilation and vascular permeability. Niacin increases plasma PGD2 and serotonin in a rat model of flush. The phenothiazine prochlorperazine, the H1, serotonin receptor antagonist cyproheptadine, and the specific serotonin receptor-2A antagonist ketanserin inhibit niacin-induced temperature increase by 90% ( n = 5, p < 0.05), 90 and 50% ( n = 3, p < 0.05), and 85% ( n = 6, p = 0.0008), respectively, in this animal model. These results indicate that niacin-induced flush involves both PGD2 and serotonin, suggesting that drugs other than ASA are required to effectively inhibit niacin-induced flush.