ACE inhibitor induced cough is mediated bya) Bradykininb) Substance-P c) Prostaglandin d) Renin
**Core Concept**
ACE inhibitors are a class of medications used to treat hypertension and heart failure by blocking the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor. However, one of the side effects of ACE inhibitors is a dry, persistent cough in some patients. The underlying mechanism of this cough involves the accumulation of bradykinin, a peptide that stimulates cough receptors in the lungs.
**Why the Correct Answer is Right**
The correct answer is **a) Bradykinin**. When ACE inhibitors block the conversion of angiotensin I to angiotensin II, they also prevent the breakdown of bradykinin. Bradykinin is a potent vasodilator and also stimulates the cough reflex by binding to its receptors in the lungs. This leads to an increase in the production of kinins, which in turn stimulates the cough center in the brain. The cough is thought to be mediated by the release of substance P from sensory neurons, which then stimulates the cough reflex.
**Why Each Wrong Option is Incorrect**
* **Option B:** Substance-P is involved in the transmission of pain and is also released from sensory neurons, but it is not the primary mediator of ACE inhibitor-induced cough.
* **Option C:** Prostaglandins are involved in various physiological processes, including inflammation and pain, but they are not directly involved in ACE inhibitor-induced cough.
* **Option D:** Renin is an enzyme involved in the renin-angiotensin-aldosterone system, but it is not directly involved in ACE inhibitor-induced cough.
**Clinical Pearl / High-Yield Fact**
Remember that ACE inhibitor-induced cough is a common side effect of this class of medications, and it is often reversible by switching to an angiotensin receptor blocker (ARB).
**Correct Answer: A. Bradykinin**