Which cell mediator of inflammation stimulates smooth muscle contraction?

RRB Nsg Superintendent -29 April 2025 (Shift-1st)

Pharmacology

Easy

Appeared in: RRB Nsg Superintendent -29 April 2025 (Shift-1st)

Explanation

Leukotrienes, specifically LTC₄, LTD₄, and LTE₄, are extremely potent mediators that cause intense and prolonged contraction of smooth muscle, particularly in the bronchioles.
This action is central to their role in bronchospasm associated with asthma and anaphylaxis.
They are significantly more powerful (100 to 1,000 times) and their effects are more sustained than histamine in causing bronchoconstriction.
Leukotrienes are derived from the lipoxygenase pathway of arachidonic acid metabolism.

Option A: While histamine does cause contraction of some smooth muscles (like bronchial smooth muscle), its primary inflammatory roles are vasodilation of arterioles and increasing vascular permeability. Its bronchoconstrictive effect is less potent and shorter-lived compared to leukotrienes.
Option B: The effects of prostaglandins are diverse. While some types (like PGF₂α) can cause smooth muscle contraction, the most prominent prostaglandins in inflammation (PGE₂ and PGI₂) primarily cause vasodilation, pain, and fever. Therefore, as a group, they are not best known for stimulating contraction.
Option C: Serotonin (5-HT) is primarily a vasoconstrictor, meaning it contracts the smooth muscle of blood vessels. However, its role in the overall inflammatory response is considered less significant than that of histamine or leukotrienes.

Visual 1: Diagram: A flowchart showing the Arachidonic Acid Metabolism pathways. This would visually separate the Cyclooxygenase (COX) pathway (leading to prostaglandins) from the Lipoxygenase pathway (leading to leukotrienes) and highlight their respective products and actions.
Visual 2: Infographic: A comparative chart illustrating the relative potency and duration of action of Histamine vs. Leukotrienes on bronchial smooth muscle, showing leukotrienes as much more powerful and long-lasting.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Inflammatory Mediators and Smooth Muscle Contraction as background academic context rather than a clinical decision trigger.
Understanding the specific roles of inflammatory mediators is crucial for nurses to comprehend the pathophysiology of diseases like asthma, allergies, and anaphylaxis.
This knowledge is essential for patient education regarding medications. For example, explaining to a patient with asthma why they are prescribed a leukotriene inhibitor (like Montelukast) in addition to an inhaler (which might be an antihistamine or beta-agonist).
What if the question asked for the mediator responsible for fever and pain? The answer would be Prostaglandins, as they act on the hypothalamus to raise the temperature set-point and sensitize nerve endings to painful stimuli.

How to Approach the Question

First, identify the key concepts in the question: 'cell mediator,' 'inflammation,' and 'stimulates smooth muscle contraction.'
The question asks for a specific function (smooth muscle contraction) of an inflammatory mediator.
Recall the primary functions of each option: Histamine (vasodilation, permeability), Prostaglandins (pain, fever, vasodilation), Serotonin (vasoconstriction), and Leukotrienes (potent smooth muscle contraction).
Compare the options based on the specific function asked. While multiple mediators might have some effect, the question seeks the one for which this is a primary and potent action.
Leukotrienes are famously known as the 'slow-reacting substance of anaphylaxis' precisely because of their powerful and sustained effect on smooth muscle, making them the best fit.

Concept Tested & Keywords

Q5paUD48LiXulkIak4LfuW