Method for determination of angiotensin-converting enzyme activity in blood and tissue by high-performance liquid chromatography

A simplified method for an angiotensin-converting Enzyme activity assay in biological samples was developed. Samples were incubated with hippurylhistidylleucine, an artificial substrate of angiotensin-converting Enzyme. The reaction was terminated by the addition of metaphosphoric acid and liberated hippuric acid in the supernatant was quantitated directly by reversed-phase high-performance liquid chromatography. Tissues were homogenized in the presence of Nonidet-P40, a detergent, and the resulting supernatant was used for the assay of tissue angiotensin-converting Enzyme activity by high-performance liquid chromatography. The present procedure made it possible to determine angiotensin-converting Enzyme activity in whole blood and the total activity in tissues. A comparative study of angiotensin-converting Enzyme activity in plasma, kidney and lung of five experimental Animals showed a high degree of variation from species to species.