Measurement of plasma renin concentration in cats by use of a fluorescence resonance energy transfer peptide substrate of renin

Abstract

Objective - To evaluate the use of a commercially available 5-carboxyfluorescein-based, intramolecularly quenched, fluorescence resonance energy transfer (FRET) peptide substrate of renin for measurement of plasma renin concentration in cats. Sample Population - Plasma samples obtained during a previous study of renal autograft ischemia-reperfusion injury in 10 cats and samples of fetal bovine serum containing recombinant human renin (rh-renin). Procedures - Experiments involving samples of fetal bovine serum containing rh-renin were conducted to identify a suitable control vehicle, optimal substrate concentration, and appropriate duration of incubation. With the use of the identified assay conditions, a standard curve was constructed to allow conversion of relative fluorescent units into values of renin concentration (ng/mL). Subsequently, plasma samples obtained from cats before and after renal autograft ischemia-reperfusion injury were assayed to determine endogenous renin concentration. Results - Under conditions of a 1:50 substrate dilution and 4-hour incubation period, the assay detected small amounts of rh-renin in fetal bovine serum. A linear relationship (R2 = 0.996) between the relative fluorescent units generated and exogenous rh-renin concentration was evident. The assay detected renin in plasma samples obtained from cats after renal autograft ischemia-reperfusion, and renin concentrations on days 1 and 2 after transplant differed significantly. Conclusions and Clinical Relevance - The study data indicated that the assay involving the FRET peptide substrate of renin is potentially a rapid and specific method for measurement of plasma renin concentration in cats.