Improvement of renin determination in human plasma using a commonly available renin standard in a radioimmunological...

A new method for the measurement of renin in human plasma is described. The method is based on the introduction of the internationally available renin standard of the Medical Research Council (MRC) London, as a calibration system. Thus, some principal disadvantages of methods expressing results in renin reaction velocity (angiotensin generation rate) only are avoided. Both renins, unknown and standard, react with a sheep substrate preparation and are handled identically throughout the whole procedure including the angiotensin I radioimmunoassay (RIA). The plasma renin concentration (PRC) is given in 10(-6) MRC-renin units (muM/ml).

the renin standard is free of angiotensin, angiotensinases, and angiotensinogen; it is stable on storage. Identical enzyme kinetics are shown for both renins. An interference between endogenous and exogenous substrate could be avoided. The potentially harmful influences of proteins from the enzyme incubation mixture of the RIA dose response curve are shown. The use of an angiotensin I calibration system could be omitted. Using a standard renin dilution from 250-0.9 muU/ml also the full biological range is covered. When giving an unrestricted diet the preliminary normal values of PRC are 21.9 +/- 12.6 muU/ml in recumbent and 40.1 +/- 19.8 muU/ml in upright position (n = 16,x +/- s, age 20-35 years). Earlier findings of age-dependency of PRC were confirmed.