Enzyme immunoassay and radioimmunoassay for plasma renin activity. I. Comparison of the methods

Sensitive and specific enzyme and radioimmunoassays have been developed for the determination of renin activity. These methods are based upon the determination of angiotensin I generated by endogenous renin and angiotensinogen. An antibody trapping technique was used, while the addition of chemicals to the plasma, used until now as inhibitors for converting enzyme and angiotensinases, was eliminated. The angiotensin I was labelled with horseradish peroxidase for enzyme immunoassay and with iodine-125 for radioimmunoassay. Antibody bound and free labelled antigen were separated from each other by a second antibody polyethyleneglycol method (enzyme immunoassay) and by charcoal-dextran adsorption (radioimmunoassay). The values of renin activity in human plasma determined by enzyme immunoassay correlated well with those obtained by radioimmunoassay.