WBR0371

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Gastrointestinal, SubCategory::Renal
Prompt	[[Prompt::A 67-year-old man presents to his physician for his annual check-up. The patient has a significant history of hypertension. A hormonal panel reveals the results shown in the table below. Which medication is the patient most likely taking to control his blood pressure? ]]
Answer A	AnswerA::Valsartan
Answer A Explanation	AnswerAExp::Valsartan is an angiotensin II receptor blocker that blocks the AT1 receptor. With the use of ARB, concentrations of renin, angiotensin I, and angiotensin II are expected to be increased.
Answer B	AnswerB::Ramipril
Answer B Explanation	AnswerBExp::Ramipril is an ACEI that blocks the conversion of angiotensin I to angiotensin II. As such, the concentration of angiotensin I is expected to increase, while the concentration of angiotensin II will decrease with ACEI.
Answer C	AnswerC::Acebutolol
Answer C Explanation	AnswerCExp::Acebutolol is a beta-blocker that has a direct effect on sympathetic receptors. Beta-blockers have a small effect on the RAAS by decreasing renin secretion.
Answer D	AnswerD::Nifedipine
Answer D Explanation	AnswerDExp::Nifedipine is a dihydropryridine calcium channel blocker that inhibits L-type calcium channels in the peripheral blood vessels.
Answer E	AnswerE::Diltiazem
Answer E Explanation	AnswerEExp::Diltiazem is a non-dihydropyridine calcium channel blocker that also inhibits L-type calcium channels in the heart and in the peripheral blood vessels.
Right Answer	RightAnswer::A
Explanation	[[Explanation:: The use of either valsartan, an angiotensin II receptor blocker (ARB) or ramipril, an angiotensin II converting enzyme inhibitor (ACEI) will stimulate renin secretion due to the interruption of angiotensin II feedback inhibition. As such, both medications significantly increase plasma renin concentration. However, ARB and ACEI act by different mechanisms to inhibit the renin-angiotensin system (RAS). Because ACEIs block the the angiotensin converting enzyme, subsequent products of the enzyme such as angiotensin II, are expected to decrease. In contrast, ARB inhibits the angiotensin II (AT1 subtype) receptor, thus inhibiting the action of angiotensin II without actually affecting its concentration or production. Given that this patient has elevated concentrations of renin, angiotensin I, and angiotensin II, he is most likely receiving an ARB. Educational Objective: Although ACEIs and ARBs inhibit the renin-angiotensin-system (RAS), they work by different mechanisms. ACEIs block the the angiotensin converting enzyme, causing angiotensin II concentrations to decrease. In contrast, ARB inhibits the angiotensin II (AT1 subtype) receptor, thus inhibiting the action of angiotensin II without actually affecting its concentration or production. References: Chen L, Kim SM, Eisner C, et al. Stimulation of renin secretion by angiotensin II blockade is Gsα-dependent. J Am Soc Nephrol. 2010; 21(8):988-992. Image courtesy of the Openstax COLLEGETM Anatomy & Physiology Textbook, licensed under Creative Commons Attribution 3.0]]
Approved	Approved::Yes
Keyword	WBRKeyword::RAAS, WBRKeyword::Renin Angiotensin aldosterone system, WBRKeyword::Renin, WBRKeyword::ACE inhibitor, WBRKeyword::ARB, WBRKeyword::Angiotensin-converting enzyme, WBRKeyword::Angiotensin receptor blocker
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