Urinalysis for detection of chemically induced renal damage (3)--Establishment and application of radioimmunoassay for lysozyme of rat urine.

The radioimmunoassay (RIA) as a high sensitive detection method for rat lysozyme (LZM) was established and applied to determine LZM excretion in urine from rats treated with tubulotoxic chemicals in order to establish a sensitive method of detecting minor renal damage. Rat LZM which showed a single protein band on sodium dodecylsulfate polyacrylamide gel electrophoresis was purified by ion-exchange chromatography and gel filtration. The assay sensitivity of the established RIA using the purified rat LZM was 4-256 ng/ml rat LZM and was about 20 times the turbidity method. The concentration of LZM in normal rat urine was 76.2 +/- 6.0 ng/ml (mean +/- SE, n = 50) using the RIA. In urine containing more than 100 ng/ml LZM, a high correlation between the values determined by the RIA and those by the turbidity method was observed. However, egg white LZM, human urinary LZM and guinea pig urinary LZM were not detectable by the RIA. Using the RIA, it was ascertained that urinary LZM excretion began to increase on day 5 in rats treated with gentamicin (15 or 30 mg/kg/day sc for 17 days), during the 6-9 h period in the rats treated with mercuric chloride (1 mg/kg sc), and during the 0-3 h period in the rats treated with p-aminophenol (1 mmol/kg sc). These significant increases in LZM excretion were not detectable by the turbidity method; therefore, it was concluded that this RIA for rat LZM was very useful for detection of minor renal damage.