A plasma inhibitor of the renin-antirenin reaction and the in vitro generation of angiotensin I.

In the course of studies designed to develop a radioimmunoassay system for the detection of renin, we have identified in human plasma a potent inhibitor that interferes with the renin-antirenin reaction. Utilizing gel filtration, this renin-antirenin inhibitory activity was found to have the same molecular size as renin substrate. However, it could be separated from renin substrate by ion-exchange chromatography. When fractions containing this activity were tested in an in vitro system containing renin and renin substrate, they were found to inhibit the generation of angiotensin I.