Measurements of enzyme activity and immunoreactivity of plasma renin. Limitations of the conventional method for assay of plasma renin catalytic activity.

Abstract

The values for "plasma renin activity", "plasma renin concentration" (both determined by the rate of angiotensin I generation) and the plasma active renin protein mass concentration (active enzyme protein measured by a direct radioimmunoassay) were compared. The values for "plasma renin activity" (angiotensin I generation from endogeneous renin substrate) and "plasma renin concentration" (angiotensin I generation from exogeneous excess of renin substrate) showed a significant correlation. However, the correlation was lost in samples with high (plasma renin activity greater than or equal to 10 micrograms/l.h) and low (plasma renin activity less than or equal to 1 microgram/l.h) renin contents. In another study, values for "plasma renin activity" were correlated with those for plasma active renin protein mass concentration, and values for "plasma renin concentration" were also correlated to those for plasma active renin protein mass concentration. However, in samples with low renin contents (plasma active renin protein mass concentration less than or equal to 20 ng/l), there was no correlation between values for "plasma renin activity" and plasma active renin protein mass concentration, although those for "plasma renin concentration" and plasma active renin protein mass concentration showed a significant correlation. These results suggest that the current method for the assay of plasma renin activity gives erroneous values for low and high plasma renin concentrations. The new radiometric method for the determination of the plasma active renin protein mass concentration seems to be applicable to plasma samples with a wide range of renin concentrations.