 Their name comes from their role in clot formation (thrombosis).Specific prostaglandins are named with a letter (which indicates the type of ring structure) followed by a number (which indicates the number of double bonds in the hydrocarbon structure).For example, prostaglandin E1 is abbreviated PGE1 or PGE1, and prostaglandin I2 is abbreviated PGI2 or PGI2.