Renal excretion and cyst accumulation of β2microglobulin in polycystic kidney disease

Abstract

To determine the extent to which proximal tubule function is altered beta 2microglobulin (beta 2m), creatinine and Na were measured in serum, urine and cyst fluid of patients with autosomal dominant polycystic kidney disease and various degrees of renal insufficiency. Fractional excretion (FE beta 2m) was 0.11 +/- 0.03% in six normal subjects and 0.13 +/- 0.05% in nine patients with serum creatinine levels less than 1.6 mg/dl. In five patients with serum creatinine levels above 3.0 mg/dl, FE beta 2m was elevated (range 3.5 to 196%) and serum levels were higher than normal (30,600 +/- 6,910 micrograms/liter vs. 1,268 +/- 111). In seven patients beta 2m levels in 33 proximal cysts (cyst/serum Na greater than 0.8) equalled those in serum (cyst/serum beta 2m 0.98 +/- 0.20), whereas in 21 distal cysts (cyst/serum Na less than 0.4) beta 2m was less than in serum (cyst/serum beta 2m 0.17 +/- 0.07). Analysis of fluid in two patients with polycystic kidney nephrectomy several weeks posttransplant indicated that proximal cyst epithelium is permeable to beta 2m, but less so than to creatinine or urea. These studies show that proximal cysts cannot develop or maintain gradients for beta 2m, whereas distal cysts maintain low levels of the protein despite end-stage renal failure. The normal FE beta 2m values in nonazotemic autosomal dominant polycystic kidney disease patients and the low distal cyst levels of beta 2m in end-stage kidneys indicate that the cystic proximal nephrons do not contribute appreciably to the final urine.(ABSTRACT TRUNCATED AT 250 WORDS)