Prostaglandin D<sub>2</sub> (or PGD<sub>2</sub>) is a prostaglandin that binds to the receptor PTGDR (DP<sub>1</sub>), as well as CRTH2 (DP<sub>2</sub>). It is a major prostaglandin produced by mast cells â recruits Th2 cells, eosinophils, and basophils. In mammalian organs, large amounts of PGD<sub>2</sub> are found only in the brain and in mast cells. It is critical to development of allergic diseases such as asthma. Research carried out in 1989' found PGD<sub>2</sub> is the primary mediator of vasodilation (the "niacin flush") after ingestion of niacin (nicotinic acid).
A 2012 research paper indicates a causal link between elevated levels of localized PGD<sub>2</sub> and hair growth inhibition. Applied topically, the researchers found PGD<sub>2</sub> prevents hair growth, and mice that were genetically inclined to produce higher levels of PGD<sub>2</sub> had inhibited hair growth. The researchers also found PGD<sub>2</sub> levels were much higher in balding scalp tissue than nonbalding scalp tissue, through increased levels of prostaglandin D2 synthase. The paper suggested that inhibition of hair growth involved binding of PGD<sub>2</sub> to a DP<sub>2</sub> receptor, and that DP<sub>2</sub> therefore would be a therapeutic target for androgenic alopecia in both men and women with hair loss and thinning. Because PGD<sub>2</sub>'s relation to asthma has been known for several years, several drugs that seek to reduce the effect of PGD<sub>2</sub> through blocking the DP<sub>2</sub> are already in clinical trials.
In silico simulations have predicted the following as potential inhibitors of PGD<sub>2</sub> synthase: