An intermediary substance or thing.
- pharmacologic mediators of anaphylaxis substances released from mast (and other) cells by the reaction of antigen and specific homocytotropic antibody on their surfaces; they include histamine, slow-reacting substance of anaphylaxis (SRS-A), bradykinin, and (in some species of animals) serotonin.
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me·di·a·tor 'mēd-ē-.āt-ər n one that mediates esp a mediating agent (as an enzyme or hormone) in a chemical or biological process <substance P, a neuropeptide \mediator of analgesic stimuli in peripheral sensory nerves (D. R. Robinson)>
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me·di·a·tor (meґde-a″tər) an object or substance that intervenes on behalf of something else, or transmits or conveys something else, such as (1) a structure of the nervous system that transmits impulses eliciting a specific response; (2) a chemical substance (neurotransmitter) that induces activity in an excitable tissue, such as nerve or muscle; or (3) a substance released from cells as the result of the interaction of antigen with antibody or by the action of antigen with a sensitized lymphocyte.Medical dictionary. 2011.