What is the effect of ACE inhibitors on the renin-angiotensin system?

ACE inhibitors are primarily designed to inhibit the activity of angiotensin-converting enzyme (ACE), which plays a crucial role in the renin-angiotensin system (RAS). By blocking ACE, these medications prevent the conversion of angiotensin I to angiotensin II. This reduction in angiotensin II levels results in decreased vasoconstriction, as angiotensin II is a potent vasoconstrictor.

Furthermore, lower levels of angiotensin II also lead to diminished stimulation of aldosterone secretion from the adrenal cortex, which in turn decreases sodium retention and fluid volume expansion. This collectively results in the therapeutic effects of ACE inhibitors, such as reducing blood pressure and alleviating heart failure symptoms.

In the context of this question, the correct answer highlights the primary action of ACE inhibitors—preventing the formation of angiotensin II, which is fundamental to understanding how these medications function within the RAS.