slow-reacting substance (SRS)

slow-re·act·ing sub·stance (SRS)

, slow-reacting substance of anaphylaxis (SRS-A) (slō-rē-ak'ting sub'stăns, an'ă-fi-lak'sis)
A leukotriene of low molecular weight released in anaphylactic shock that produces slower and more prolonged contraction of muscle than does histamine; it is active in the presence of antihistamines (but not epinephrine) and seems not to occur preformed in mast cells, but as a result of an antigen-antibody reaction on the granules.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012