Which of the following is a substance that decreases pain transmission and causes an inflammatory response?

AIIMS BBSR SNO - 2019

Applied Physiology

Hard

Appeared in: AIIMS BBSR SNO - 2019

Explanation

Prostaglandins are lipid compounds released at the site of tissue damage or infection.
They are potent mediators of inflammation, causing vasodilation (redness, heat) and increased vascular permeability (swelling).
Prostaglandins do not decrease pain; they increase pain by sensitizing peripheral nerve endings (nociceptors) to other stimuli like bradykinin. This effect is called hyperalgesia (an increased sensitivity to pain).
Because of this dual role in promoting both inflammation and pain, they are the target of nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and aspirin.

Option A: Substance P is a neurotransmitter that transmits pain signals to the brain, thereby increasing the sensation of pain. It is also pro-inflammatory. It does not decrease pain.
Option B: Endorphins are endogenous opioids that act as the body's natural painkillers. They inhibit pain transmission. However, they do not cause inflammation; they have anti-inflammatory effects.
Option D: Histamine is a key mediator of acute inflammation and allergic reactions. It causes vasodilation, swelling, and also excites nerve endings, leading to itching and pain. It does not decrease pain.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mediators of Pain and Inflammation as background academic context rather than a clinical decision trigger.
Understanding these mediators is fundamental to pharmacology. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, naproxen, and aspirin work by inhibiting the cyclo-oxygenase (COX) enzymes, which blocks the production of prostaglandins, thereby reducing both pain and inflammation.
Opioid analgesics like morphine mimic the action of endogenous endorphins to provide powerful pain relief.
What if a patient has a peptic ulcer? In this case, prescribing NSAIDs is risky because prostaglandins also have a protective role in the stomach lining. Blocking them can worsen ulcers. A COX-2 selective inhibitor might be a safer alternative.

How to Approach the Question

First, analyze the question and break it down into its core requirements. The question asks for a substance with two specific functions: 1) an effect on pain transmission and 2) an effect on inflammation.
Carefully read the specific effects required: 'decreases pain transmission' and 'causes an inflammatory response'.
Evaluate each option against these two criteria based on your knowledge of physiology.
Recognize that Endorphins decrease pain but are anti-inflammatory. Recognize that Prostaglandins, Substance P, and Histamine are pro-inflammatory but also increase pain.
Identify the contradiction in the question: no option fits both criteria perfectly as stated. In such cases, consider the possibility of a typo in the question. The most likely intended question is about a substance that increases pain and causes inflammation.
With the corrected premise, evaluate the options again. Prostaglandin is the most classic and direct answer for a substance that is both pro-inflammatory and sensitizes nerves to pain, and is the target of common medications for both symptoms.

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