Measurement of plasma renin activity using fluorescent substrate renin

: Direct chromatographic method for measuring renin activity by high-performance liquid chromatography has been developed. The method is based on enzymatic hydrolysis of a new fluorescent substrate renin with formation of fluorescent angiotensin I (fAI). The content of fAI is evaluated by a calibration curve reflecting a linear relationship between the ratio of fAI and internal standard areas and the amount of resultant fA1 in reaction mixture. 100 microliters plasma is needed for analysis. After 1-h incubation at 37 degrees C the reaction mixture is introduced directly into chromatographic system with a precolumn. Acetonitrile gradient in 0.05 M Tris-TPU buffer (pH 8.0) allows a satisfactory separation of hydrolysis products. The sensitivity of the method is 100 pg fAI/ml. The method adequately reflects species characteristics of plasma renin activity and its changes caused by stimulation of renin secretion, is characterized by higher selective activity than radioimmunoassay, and is more rapid.