Angiotensin-I converting enzyme activity in the sera of captopril-treated hypertensive patients

The blood pressure and serum angiotensin-I converting enzyme (SACE) activity were measured in captopril-treated hypertensive patients at frequent intervals. Inhibition of SACE was observed in patients responding to the treatment with lowering of blood pressure as well as in nonresponding cases. It was therefore concluded that a mechanism not depending on the formation of angiotensin-II by ACE is responsible for the high blood pressure persisting in the captopril treated nonresponding hypertensive patients. SACE activity in sera of captopril-treated patients recovers from inhibition when stored in frozen state at -20 degrees c. An apparent dissociation was therefore observed when regeneration of SACE activity during storage of sera was not taken into account. Meaningful activities are therefore obtained only if the assay is performed without prolonged storage.