What is the mechanism of action of ACE inhibitors?

ACE inhibitors work by inhibiting the enzyme angiotensin-converting enzyme (ACE), which is responsible for converting angiotensin I, an inactive precursor, into angiotensin II, a potent vasoconstrictor. By blocking this conversion, ACE inhibitors lead to decreased levels of angiotensin II in the bloodstream. This results in several therapeutic effects, including vasodilation, reduced blood pressure, and decreased workload on the heart. Additionally, lower levels of angiotensin II lead to reduced secretion of aldosterone, further decreasing sodium and water retention, which can be beneficial in the management of conditions such as hypertension and heart failure.

The other options describe mechanisms of action unrelated to ACE inhibitors. For instance, blocking sodium reabsorption in the kidney is primarily associated with diuretics, while competing with serotonin at receptor sites refers to certain antidepressants, and stimulating beta-adrenergic receptors relates to sympathomimetics. These mechanisms do not pertain to the function of ACE inhibitors.