In a study of the renin-angiotensinogen interaction, under various conditions of time, temperature and concentration of renin and angiotensinogen, an indirect method for the quantitative determination of renin in the kidneys and of angiotensinogen in the serum of nine species was developed. This method involves the bioassay of the angiotensin formed as a result of the incubation in vitro of purified renal extracts with homologous serum or plasma. Renin and angiotensinogen, at the concentrations of the latter existing in the serum of the various species, were both found to be rate-determining in the process of angiotensin formation. There were striking differences in the concentration of renin in normal kidneys of the various species, with rabbit kidney having more than 70 times as much renin as human kidney. A pronounced increase of renin was found in the ischemic kidney of dogs with experimental renal hypertension. An exceptionally high concentration of angiotensinogen was present in normal human serum compared to that of the eight other species investigated. The results of the previous and present determinations of the renin concentration in the kidneys of various species differ considerably because the former method depended upon a heterologous renin-angiotensinogen reaction, in vivo, while the present evaluation is based on a homologous renin-angiotensinogen reaction in vitro.

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