Platelet-activating factor (PAF, AGEPC, acetyl-glyceryl-ether-phosphorylcholine) is a potent phospholipid activator and mediator of many leukocyte functions, including platelet aggregation, inflammation, and anaphylaxis. It is an important mediator of bronchoconstriction. It causes platelets to aggregate and blood vessels to dilate so is important to the process of hemostasis. The PAF receptor (Ye RD et al, 1991) shows structural characteristics of the rhodopsin gene family and binds platelet-activating factor (PAF). The activity of this receptor is mediated by coupling with the G protein alpha q subunit which stimulates PLC-beta which can cleave PIP2 to form secondary messengers (Deo DD et al, 2004).