**Core Concept**
The preformed mediator of inflammation refers to a substance that is stored in cells and released in response to an inflammatory stimulus, playing a crucial role in initiating the inflammatory response. These mediators are pre-formed and stored in secretory vesicles, allowing for a rapid response to injury or infection.

**Why the Correct Answer is Right**
The correct answer is histamine, which is a preformed mediator of inflammation stored in mast cells and basophils. When these cells are activated, histamine is released and binds to specific receptors on the surface of nearby cells, causing vasodilation, increased vascular permeability, and smooth muscle contraction. This leads to the characteristic symptoms of inflammation, including redness, swelling, and pain.

**Why Each Wrong Option is Incorrect**
* **Option A:** Bradykinin is a mediator of inflammation, but it is formed through the kallikrein-kinin system, which is an enzyme-mediated pathway, not a preformed mediator.
* **Option B:** Prostaglandins are also mediators of inflammation, but they are synthesized through the cyclooxygenase pathway from arachidonic acid, which is not a preformed mediator.
* **Option C:** Leukotrienes are another type of mediator of inflammation, but they are also synthesized through the lipoxygenase pathway from arachidonic acid, not a preformed mediator.

**Clinical Pearl / High-Yield Fact**
Histamine is a key player in the inflammatory response and is also involved in allergic reactions, such as anaphylaxis. Antihistamines, which block histamine receptors, are commonly used to treat allergic symptoms.

**Correct Answer: C. Histamine**