In vivo, when alacepril undergoes deacetylation, it loses a molecule similar to the amino acid phenylalanine which transforms it into captopril. Captopril then provides its blood pressure lowering effect through two way. First, it inhibits the conversion of angiotensin 1, a precursor molecule, to angiotensin II, a vasoconstrictor that narrows blood vessels. Secondly, captopril prevents the breakdown of bradykinin, a vasodilator peptide that naturally relaxes blood vessels.