Immediate transient type of increase vascular permeability in acute inflammation –
## **Core Concept**
The question pertains to the immediate transient type of increase in vascular permeability observed in acute inflammation. This phenomenon is primarily mediated by **histamine** and other chemical mediators released from mast cells and basophils. The increase in vascular permeability leads to the characteristic signs of inflammation, including edema.
## **Why the Correct Answer is Right**
The correct answer, **histamine**, is right because it causes a rapid and transient increase in vascular permeability. Histamine acts on **H1 receptors** located on the endothelial cells of blood vessels, leading to the contraction of these cells and the formation of gaps between them. This results in the leakage of fluid and proteins into the interstitial space, contributing to edema and other inflammatory manifestations. Histamine's effects are immediate but short-lived, fitting the description of an "immediate transient" increase in vascular permeability.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although bradykinin does increase vascular permeability, its action is not as immediate or transient as histamine's. Bradykinin's effects are more sustained and part of the kinin-kallikrein system.
- **Option B:** This option is incorrect because leukotrienes do increase vascular permeability but are more involved in the late phase of inflammation and have a more sustained effect compared to histamine's immediate action.
- **Option D:** This option is incorrect because prostaglandins have a variety of effects on inflammation, including influencing vascular permeability indirectly, but they are not primarily responsible for the immediate transient increase in vascular permeability.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **histamine-mediated effects** can be effectively counteracted by antihistamines, which are commonly used to treat allergic reactions characterized by increased vascular permeability, such as urticaria and anaphylaxis.
## **Correct Answer:** .