<prompt> Which one of the following is NOT true about chemical mediators:Leukotrienes are formed by lipo-oxygenase pathwayHistamine is a preformed chemical mediatorProstaglandin causes vasoconstriction at the site of inflammationThromboxane A2 is associated with platelet aggregation  <response>: Leukotrienes are formed by Lipo-oxygenase , Whereas, prostaglandins are formed by cyclo-oxygenase. PGs causes vasodilation. 