Mechanism of action of Telmisaan is: September 2010
**Core Concept**
Telmisartan, a medication used in the treatment of hypertension and heart failure, acts through a specific mechanism that involves the renin-angiotensin-aldosterone system (RAAS). The RAAS plays a crucial role in regulating blood pressure and fluid balance in the body. Telmisartan selectively blocks the action of angiotensin II at its receptor sites, leading to vasodilation and decreased blood pressure.
**Why the Correct Answer is Right**
Telmisartan is an angiotensin II receptor antagonist (ARB), which means it competes with angiotensin II for binding to the angiotensin II type 1 (AT1) receptor. By occupying the receptor sites, telmisartan prevents angiotensin II from exerting its vasoconstrictive and aldosterone-stimulating effects. This results in decreased peripheral resistance, reduced blood pressure, and decreased aldosterone-mediated fluid retention. The blockade of AT1 receptors also leads to an increase in the levels of bradykinin and other vasodilatory peptides, further contributing to the antihypertensive effect.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as telmisartan does not have a significant effect on the sympathetic nervous system or the release of norepinephrine.
**Option B:** This option is incorrect as telmisartan does not act as a beta-blocker or have a significant effect on the heart rate or contractility.
**Option C:** This option is incorrect as telmisartan does not have a direct effect on the kidneys or the renin-angiotensin system through its action on the RAAS.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that ARBs like telmisartan are not suitable for patients with bilateral renal artery stenosis, as they can worsen renal function due to the lack of compensatory increase in renin release.
**Correct Answer: C. Angiotensin II receptor antagonist**