Measurement of the Rat Urinary Plasminogen Activator (Esterase A) by Direct Radioimmunoassay in Urine and Tissue

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Abstract
Rat urinary esterase A, a plasminogen activator with kininogenase activity, was recently purified and characterized. A sensitive radioimmunoassay [RIA] for esterase A was developed. This assay uses a rabbit antiserum in a final dilution of 1:160,000 and the purified enzyme was labeled with 125I using a lactoperoxidase method. It detects 80 pg of immunoreactive [Ir] material/tube. This antiserum has some cross-reactivity with rat urinary kallikrein (.apprxeq. 5%) but a previously characterized tissue kallikrein antiserum has negligible cross-reactivity with the urinary esterase A in the assays. Therefore, kallikrein levels are measured simultaneously in all samples to obtain accurate levels of Ir esterase A. Dilutions of urine or tissue homogenates showed complete parallelism with esterase A standard curves. No cross-reactivity with dog, human or monkey urine was seen. The recovery of esterase A from rat urine was 99.7 .+-. 3.5%. Intra- and between-assay errors were 6.5 and 11.2%, respectively. Ir esterase A was measured and compared with kallikrein levels in rat urine, kidney, pancreas, submandibular gland, descending colon and ileum. The urinary esterase A excretion rate was reduced significantly in rats on a high Na, compared with a low Na diet, but not significantly increased above control by the latter. Nonetheless, a significant correlation between urinary kallikrein and esterase A excretion rate was present. This RIA can now be used to measure esterase A levels in urine and tissue as questions have arisen about its regulation and functional significance.

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