MEASUREMENT OF URINARY KALLIKREIN ACTIVITY BY KININ RADIOIMMUNOASSAY

We have established a simplified assay system for the measurement of urinary kallikrein activity by utilizing the sensitive and specific radioimmunoassay system of kinins previously reported from our laboratory. Kinins were generated by incubating urine samples (50μl) with kininogen (1500 ng) in the presence of kininase inhibitors, and the generated kinins were measured by radioimmunoassay. Since the cross reactivity of kininogen in the kinin radioimmunoassay system was not recognized at dose up to 1.0 μg, the amount of untreated kininogen in the radioimmunoassayed samples did not interfere with the measurement of kinins. This eliminated the necessity for a kininogen extraction procedure. A good linear correlation (r=0.939, p<0.001) was observed between the urinary kallikrein activity determined by this assay system (kininogenase activity) and that by esterolytic activity. Urinary kallikrein activity was 3.3 ± 0.9 μg/min/24hour urine (mean ± SEM), 1.4 ± 0.4 μg/min/24hour urine and 0.25 ± 0.06 μg/min/24hour urine in 6 normal subjects, 7 patients with non-complicated essential hypertension and 4 patients with chronic renal failure, respectively. Thus, urinary kallikrein activity was significantly lower in the patients with essential hypertension (p<0.05) and the patients with chronic renal failure (p <0.01) than the normal subjects.