A direct radioimmunoassay of rat urinary kallikrein and comparison with other measures of urinary kallikrein activity.

A highly sensitive radioimmunoassay for rat urinary kallikrein (minimal detectable amount, 40 pg/tube) has been developed. The assay uses a sheep antibody (Keq = 3.25 X 10(10)M-1) against purified Sprague-Dawley rat urinary kallikrein in a final dilution of 1 : 1,200,000. The assay incorporates a convenient and inexpensive PEG technique for separation of free from bound antigen. Parallel standard curves with rat urine or kidney homogenates were obtained. No cross-reactivity with human or dog urine samples or purified human urinary kallikrein was seen. Correlations among this assay, an esterolytic method, and a kininogenase radioimmunoassay for kallikrein were highly significant, with only the esterolytic assay demonstrating any significant nonspecificity. The radioimmunoassay can detect changes in urinary kallikrein levels produced by a maneuver known to alter urinary kallikrein excretion.