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The present paper is concerned with studies on some problems in the measurement of plasma renin activity, i.e., inhibition of angiotensinase activity, some properties of renin activity, and concentration and purification of angiotensin from plasma. Renin was extracted from hog kidney by the method of Haas et al. (1965). Angiotensinase activity in the extract was well inhibited not only in neutral solution but also in acid solution with the aid of DFP. For the inactivation of plasma angiotensinase, addition of EDTA and DFP was employed rather than acid treatment. Addition of the agents inhibited the activity almost completely at a pH below 5.5. Although it appeared to us that hog renin activity was highest at pH 6, incubation for the determination of renin activity was carried out at pH 5.5, because angiotensinase was still active over pH 6. Angiotensin was semi-purified from plasma before the assay with a combination of n-butanol and water extraction, and ion exchange chromatography. The mean recovery of added angiotensin was 70 per cent in the purification procedure.
Nigawara et al. (1972) studied this question.