Spiraprilat, the active metabolite of spirapril, competes with angiotensin I for binding at the angiotensin-converting enzyme, blocking the conversion of angiotensin I to angiotensin II. Inhibition of ACE results in decreased plasma angiotensin II. As angiotensin II is a vasoconstrictor and a negative-feedback mediator for renin activity, lower concentrations result in a decrease in blood pressure and stimulation of baroreceptor reflex mechanisms, which leads to decreased vasopressor activity and to decreased aldosterone secretion. Spiraprilat may also act on kininase II, an enzyme identical to ACE that degrades the vasodilator bradykinin.
Spirapril is an angiotensin-converting enzyme (ACE) inhibitor. ACE is a peptidyl dipeptidase that catalyzes the conversion of angiotensin I to the vasoconstrictor substance, angiotensin II. By blocking ACE, spirapril decreases angiotensin II which is a vasoconstrictor and inducer of aldosterone. So by inhibiting the enzymes, aldosterone secreation is decreased (so less sodium is reabsorbed) and there is a decrease in vasoconstriction. Combined, this leades to a decrease in blood pressure.
Hepatic. Converted to spiraprilat following oral administration.