Antihypertensive Drugs: Angiotensin-Converting Enzyme Inhibitors

ACE degrades bradykinin, an endogenous vasodilator that releases nitric oxide and prostacyclin to relax blood vessels. ACE inhibitors slow bradykinin degradation, increasing its availability for vasodilation. This enhanced bradykinin activity relaxes smooth muscle cells in blood vessels, contributing to reduced blood pressure and improved blood flow management.

Angiotensin II is a potent vasoconstrictor that narrows blood vessels, increasing resistance to blood flow and elevating blood pressure. It also stimulates aldosterone production, encouraging kidney cells to reabsorb more sodium and water from urine, thereby increasing blood volume and pressure. These dual mechanisms make angiotensin II a critical regulator of hypertension and regulation of blood pressure.

ACE inhibitors block the conversion of angiotensin I to angiotensin II by inhibiting angiotensin-converting enzyme activity. With reduced angiotensin II levels, blood vessels dilate and blood pressure decreases. Additionally, lower angiotensin II curtails aldosterone production, prompting the kidneys to excrete more sodium and water, further reducing blood volume and pressure.

ACE inhibitors are categorized into three structural groups based on their chemical composition. Sulfhydryl-containing ACE inhibitors like captopril have a sulfhydryl group. Dicarboxylate-containing ones, such as enalapril and lisinopril, contain two carboxylate groups. Phosphorus-containing ACE inhibitors like fosinopril feature a phosphonate group instead.

ACE is abundant in lung endothelial cells and is a vital component of the renin-angiotensin-aldosterone system. It converts the inactive decapeptide angiotensin I into the active octapeptide angiotensin II, a potent vasoconstrictor. ACE also degrades bradykinin, reducing its vasodilatory effects on blood vessels.

Angiotensin II stimulates aldosterone production, which increases sodium and water reabsorption from urine. When ACE inhibitors reduce angiotensin II levels, aldosterone production decreases. This prompts the kidneys to excrete more sodium and water, lowering blood volume and blood pressure through enhanced renal elimination.

ACE inhibitors work through two complementary mechanisms. First, they prevent angiotensin II formation, allowing blood vessels to dilate and reducing vascular resistance. Second, they slow bradykinin degradation, enhancing its vasodilatory effects. Together, these actions decrease blood pressure by reducing both vessel constriction and blood volume through increased sodium and water excretion.