How do ACE inhibitors affect renal function in patients with renal artery stenosis?

ACE inhibitors, such as lisinopril or enalapril, inhibit the enzyme that converts angiotensin I to angiotensin II. Angiotensin II is a potent vasoconstrictor, and it plays a critical role in maintaining glomerular filtration rate (GFR) in conditions of renal artery stenosis. In patients with renal artery stenosis, there is a reduction in blood flow to one kidney, causing the affected kidney to rely on angiotensin II to constrict the efferent arterioles. This constriction helps to maintain intraglomerular pressure and support GFR despite the reduced perfusion.

When ACE inhibitors are administered, they lower levels of angiotensin II. This reduction leads to decreased constriction of the efferent arterioles, ultimately causing a decrease in GFR. Consequently, in the setting of renal artery stenosis, the use of ACE inhibitors can lead to deterioration in renal function and a reduction in GFR, making it crucial to monitor renal function closely in these patients.