A 55-year-old man with diabetic nephropathy is started on an ACE inhibitor. One week later his serum creatinine has risen from 1.2 to 1.5 mg/dL. Which hemodynamic change explains this rise?

• A Constriction of the afferent arteriole reducing intraglomerular hydrostatic pressure
• B Elevation of glomerular capillary oncotic pressure from hemoconcentration
• C Increase in the filtration coefficient due to mesangial relaxation
• D Dilation of the efferent arteriole lowering glomerular capillary hydrostatic pressure ✓

Explanation

Angiotensin II preferentially constricts the efferent arteriole, maintaining glomerular capillary hydrostatic pressure and therefore GFR when perfusion is compromised. Blocking angiotensin II dilates the efferent arteriole, dropping intraglomerular pressure and lowering GFR despite preserving or increasing total renal plasma flow. Option A describes NSAID-induced afferent constriction, a different drug class with the same net fall in GFR.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

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