Which of the following are slow reacting substances of anaphylaxis?
**Core Concept**
The slow-reacting substances of anaphylaxis are a group of lipid mediators involved in the pathophysiology of allergic reactions. These substances are produced by the action of phospholipase A2 on membrane phospholipids, leading to the formation of arachidonic acid and subsequent production of leukotrienes.
**Why the Correct Answer is Right**
The slow-reacting substances of anaphylaxis, specifically leukotrienes, are produced by the action of 5-lipoxygenase on arachidonic acid. This leads to the formation of leukotriene C4, which is then converted to leukotriene D4 and leukotriene E4 by leukotriene C4 synthase and leukotriene D4 synthase, respectively. Leukotrienes cause bronchoconstriction, increase vascular permeability, and promote mucus production, contributing to the symptoms of anaphylaxis.
**Why Each Wrong Option is Incorrect**
**Option A:** Histamine is a fast-reacting substance of anaphylaxis, not a slow-reacting substance. It is released from mast cells and basophils during anaphylactic reactions, causing vasodilation, increased vascular permeability, and smooth muscle contraction.
**Option B:** Bradykinin is a peptide involved in the kinin-kallikrein system, which contributes to the inflammation and edema associated with anaphylaxis. However, it is not considered a slow-reacting substance of anaphylaxis.
**Option C:** Prostaglandins are another group of lipid mediators involved in inflammation and pain. While they are produced during anaphylactic reactions, they are not classified as slow-reacting substances of anaphylaxis.
**Clinical Pearl / High-Yield Fact**
Leukotrienes are a key component of the allergic response and play a critical role in the pathophysiology of asthma. Inhibitors of 5-lipoxygenase, such as zileuton, are used to treat asthma by reducing leukotriene production.
**Correct Answer:** C. Leukotrienes.