A 58-year-old man with bilateral renal artery stenosis is started on an ACE inhibitor and his serum creatinine rises promptly from 1.2 to 2.6 mg/dL. Which hemodynamic change best explains the fall in GFR?

• A Constriction of the afferent arteriole reducing renal plasma flow
• B Reduced plasma oncotic pressure raising the net filtration pressure
• C Increased mesangial cell relaxation expanding the filtration surface
• D Loss of angiotensin II mediated efferent arteriolar tone, lowering glomerular capillary hydrostatic pressure ✓

Explanation

In bilateral renal artery stenosis, GFR is maintained by angiotensin II constricting the efferent arteriole, which raises glomerular capillary hydrostatic pressure despite low perfusion. Blocking ACE removes this efferent tone, so glomerular hydrostatic pressure falls and GFR drops out of proportion to any change in renal plasma flow. Afferent constriction is not produced by ACE inhibitors, and mesangial relaxation would tend to raise, not lower, the filtration coefficient.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.