A 25-year-old woman presents with hypertension and bilateral abdominal bruits. What is the most likely acute effect of ACE inhibitor treatment on her renal function?

In this scenario, the 25-year-old woman presents with hypertension and bilateral abdominal bruits, which may indicate renal artery stenosis. In such cases, the kidneys may be relying on the constriction of the efferent arterioles to maintain adequate glomerular pressure and filtration rate due to reduced blood flow from the renal arteries.

When an ACE inhibitor is administered, it leads to the inhibition of angiotensin II production. Angiotensin II is a potent vasoconstrictor, particularly of the efferent arterioles of the glomeruli. By dilating these arterioles, ACE inhibitors can reduce the pressure in the glomeruli, which can lead to a decrease in glomerular filtration rate (GFR). This effect is particularly pronounced in patients who have renal artery stenosis, where the baseline efferent vasoconstriction is necessary to preserve GFR.

Thus, the most likely acute effect of ACE inhibitor treatment in this patient would be a decreased glomerular filtration rate due to the dilation of the efferent arterioles. This is a critical concept in understanding how ACE inhibitors affect renal function, especially in the context of conditions like renal artery stenosis.