Prostaglandin D₂ is a prostaglandin

Prostaglandin

A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....

 that binds to the receptor PTGDR, as well as CRTH2. It is a major prostaglandin produced by mast cells – recruits Th2 cells, eosinophils, basophils. In mammalian organs, large amounts of PGD₂ are found in the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

, in mast cells and found nowhere else. It is critical to development of allergic

Allergy

An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...

 diseases such as asthma

Asthma

Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...

.

Effects

• Causes a contraction of the bronchial
  Bronchus
  A bronchus is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles....
  
   airways. The concentration of PGD₂ in asthma-patients is 10 times higher than in control patients, especially after it is brought into contact with allergens.
• Involved in the regulation of reducing body temperature in sleep, and acts opposite to prostaglandin E2.
• Causes Vasodilation
  Vasodilation
  Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...