Determination of rat beta 2-microglobulin in urine and in serum. II. Application of its urinary measurement to selected nephrotoxicity models.

beta 2-microglobulin (beta 2-m) was measured in the urine of rats by a specific immunoassay based on latex particles agglutination. The excretion of this protein was compared to the excretion of the enzyme beta-N-acetyl-D-glucosaminidase (NAG), albumin and amino acids in rats treated with either a single dose of sodium chromate (5 and 10 mg kg-1), repeated doses of gentamicin (5 and 20 mg kg-1), or cadmium (1 mg kg-1), and in aging rats (from 2 to 20 months). All treatments resulted in an early increased excretion of beta 2-m indicative of functional alterations of the proximal tubular cells. An increased NAG excretion was observed only at the highest dose of chromate and in the cadmium model but the relative increases of beta 2-m were much larger (up to 200 times the control values against four times the control values for NAG). From 2 to 20 months of age, urinary beta 2-m increases by a factor of four. Aminoacids excretion showed little sensitivity in the various models. Albumin showed little variations in purely tubular or in the tubular phase of renal injury but the chronic progressive nephrosis of aging rats caused a 40-fold increase in its excretion between 2 and 20 months of age. Therefore urinary beta 2-m, albumin and albumin/beta 2-m ratio provide useful tools in the assessment of nephrotoxicity and of its mechanisms in various experimental models.