Renal handling of beta2-microglobulin in experimental renal disease

Renal extraction and urinary excretion of 125I-labelled beta2-microglobulin was studied in rats. The effect of ischaemic renal injury, experimental pyelonephritis, and unilateral nephrectomy was investigated. The tubular secretion of o-iodohippurate (OIH) was measured for comparison. The urinary excretion was calculated as the ratio between the clearance of protein and the glomerular filtration rate. The glomerular filtration rate was estimated as clearance of polyethylene glycol (PEG 1000). The renal arteriovenous concentration difference was lower for beta2-microglobulin than for PEG 1000 IN ALL THE EXperimental groups. In unilateral renal disease the beta2-microglobulin excretion of the intact kidneys was similar to that of the diseased kidneys. A significant differences was noted only after ischaemic renal injury. The same was found for OIH. After removal of the intact kidneys the excretion of beta2-microglobulin increased about 10-fold in pyelonephritic animals and 2- to 30-fold in animals with ischaemic renal injury. One hour after unilateral nephrectomy in normal animals the ratio increased about 50 per cent. The tubular secretion of OIH did not change noticeably. It is concluded that the glomerular filtration is a main step in the intrarenal catabolism of beta2-microglobin and that its urinary excretion is considerably influenced by a reduction in the functioning kidney mass.