Decrease of serum angiotensin converting enzyme activity after discontinuation of captopril treatment.

Serum ACE activity increased as expected about three-fold following six weeks of captopril (30 mg/kg/day) treatment in Wistar rats (n = 9). The effect on serum and lung ACE activity and concentration, respectively, was studied after captopril discontinuation. Serum ACE activity was measured at start and 3, 6, and 12 days after captopril withdrawal. The approximal half-life of serum ACE activity was 72 hours as judged from the decrease rate after stimulated ACE biosynthesis induced by captopril. No differences in lung plasma membranes and lung homogenate ACE concentrations between treated and untreated rats were observed 12 days after discontinuation of captopril treatment. Serum ACE activity remained unchanged in the control rats (n = 9). We conclude that induction of ACE biosynthesis in the rat is reversible after withdrawal of captopril.