[A study of albumin degradation in kidney lysosomes in the nephrotic rat]

Majority of albumin, filtered through the glomerulus, is absorbed and degraded in the renal proximal tubule. Hypoalbuminemia in nephrotic syndrome may occur because of increased albumin loss into the urine and also the increased rate of albumin degradation in the tubule cells. The present study is carried out in an attempt to elucidate the role of kidney lysosomes on albumin degradation in nephrotic rat. Nephrotic rat was induced by intraperitoneal injection of puromycin aminonucleoside and lysosomes were prepared from rat kidney cortex by Percoll gradient centrifugation of Ca2(+)-treated postnuclear supernatant. In fact, immunoblot analysis of SDS polyacrylamide gel electrophoresis of kidney lysosomal proteins revealed the presence of immunoreactive protein bands, corresponding to the endogenous albumin as well as small-molecular degradative intermediates. Albumin content of kidney lysosomal proteins, which was 15.4 +/- 1.5 mg/g protein in control rat, was measured by densitometer to be increased more than tenfold in nephrotic rat. These results suggest that kidney lysosomes play an important role of albumin degradation especially in nephrotic syndrome.