[Studies on experimental renal damage in rats. II. beta 2-microglobulin: purification, radioimmunoassay, and urine and serum levels in tubular nephropathy].

Beta 2-Microglobulin (beta 2-M) was purified from the urine of rats treated with cephaloridine by a combination of ammonium sulfate precipitation, gel chromatography, ion exchange chromatography, zone electrophoresis, and isoelectric focusing. The protein thus obtained was identified as beta 2-M by its molecular weight, electrophoretic mobility, and amino acid composition and was confirmed as a single protein through polyacrylamide gel electrophoresis, Ouchterlony immunodiffusion analyses, and immunoelectrophoresis using rabbit anti-rat beta 2-M sera. A radioimmunoassay was developed for the measurement of serum and urine beta 2-M levels. In rats given gentamicin (20 or 80 mg/kg/day, s.c.) for 10 days, serum beta 2-M was increased simultaneously with changes in common renal function parameters such as serum urea nitrogen, creatinine, and urinary protein. Urinary beta 2-M was elevated from the early stage of nephropathy and correlated with renal morphological change, indicating that urinary beta 2-M can be used as a sensitive and valuable index of renal tubular damage.