This document discusses mediators of inflammation, specifically histamine and serotonin. It notes that mediators can be produced locally by cells or derived from plasma, and act to initiate, regulate and sustain inflammatory reactions. Histamine and serotonin are classified as vasoactive amines that are among the first mediators released during inflammation. Histamine is derived from the amino acid histidine and is stored in mast cells, basophils and platelets. It acts to increase vascular permeability and vasodilation, causing wheal and flare reactions, itching, pain and bronchial asthma. Serotonin has similar but less potent actions than histamine and is stored in platelets and mast cells. Both mediators play important roles in initiating and regulating