Measurement of Kallikrein Activity in Urine of Rats and Man Using a Chromogenic Tripeptide Substrate. Validation of the Amidolytic Assay by Means of a Bradykinin Radioimmunoassay

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Abstract
Urinary kallikrein activity in rats and man was measured by an amidolytic assay using the chromogenic tripeptide D-valyl-leucyl-arginine-p-nitroanilide (S 2266). The sensitivity of the assay permits the measurement of 3.5-250 mKU [millikallikrein units] of purified porcine pancreatic kallikrein. The intraassay coefficient of variation [CV] was 1.6 .+-. 0.3% and the interassay CV 7.4 .+-. 0.9%. No changes in kallikrein activity were found in urine samples kept for 7 days at 4.degree. C or 14 mo. at -20.degree. C. Repeated freezing and thawing reduced kallikrein activity. Kallikrein activity of the same urine samples was estimated by means of a bradykinin radioimmunoassay, which determines the kinins released during incubation of urine with partially purified dog kininogen (kininogenase activity). The urinary kallikrein activity assayed by these 2 methods showed a high correlation with coefficients of r = 0.9314 for rat urine (P < 0.001) and r = 0.8002 for human urine (P < 0.001).