Prostaglandin D2 (PGD2) is the major eicosanoid product of mast cells and is released in large quantities during allergic and asthmatic anaphylaxis.[1] Mastocytosis patients produce excessive amounts of PGD2, which causes vasodilation, flushing, hypotension, and syncopal episodes.[1] PGD2 is also produced in the brain via an alternative pathway involving a soluble, secreted PGD-synthase also known as β-trace.[2],[3] In the brain, PGD2 produces normal physiological sleep and lowering of body temperature.[2],[3] Further pharmacological actions include inhibition of platelet aggregation and relaxation of vascular smooth muscle.[4] PGD2 inhibits human ovarian tumor cell proliferation with an IC50 of 6.8 μM.[5]

Reference:
[1]. Roberts, L.J., II, and Sweetman, B.J. Metabolic fate of endogenously synthesized prostaglandin D2 in a human female with mastocytosis. Prostaglandins 30(3), 383-400 (1985).
[2]. Hayaishi, O. Sleep-wake regulation by prostaglandins D2 and E2. J. Biol. Chem. 263(29), 14593-14596 (1988).
[3]. Onoe, H., Ueno, R., Fujita, I., et al. Prostaglandin D2, a cerebral sleep-inducing substance in monkeys. Proc. Natl. Acad. Sci. U.S.A. 85(11), 4082-4086 (1988).
[4]. Giles, H., and Leff, P. The biology and pharmacology of PGD2. Prostaglandins 35(2), 277-300 (1988).
[5]. Kikuchi, Y., Kita, T., Hirata, J., et al. Preclinical studies of antitumor prostaglandins by using human ovarian cancer cells. Cancer Metastasis Rev. 13(3-4), 309-315 (1994).