Final answer:
Angiotensin-converting enzyme (ACE) inhibitors like captopril block the formation of angiotensin II, reducing vasoconstriction.
Step-by-step explanation:
Angiotensin-converting enzyme (ACE) inhibitors like captopril block the formation of angiotensin II, reducing vasoconstriction. Angiotensin II is a potent vasoconstrictor that constricts blood vessels, increasing systemic blood pressure. By inhibiting the production of angiotensin II, ACE inhibitors prevent vasoconstriction, thereby reducing blood pressure.