Renal Handling of β₂-Microglobulin in Experimental Renal Disease

Abstract

Renal extraction and urinary excretion of ¹²⁵I-labelled β₂-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 β₂-microglobulin than for PEG 1000 in all the experimental groups. In unilateral renal disease the β₂-microglobulin excretion of the intact kidneys was similar to that of the diseased kidneys. A significant difference was noted only after ischaemic renal injury. The same was found for OIH. After removal of the intact kidneys the excretion of β₂-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 β₂-microglobulin and that its urinary excretion is considerably influenced by a reduction in the functioning kidney mass.

Key Words:

• β₂-microglobulin
• proteinuria
• renal disease
• experimental
• renal function