Micropuncture study of tubular transport of albumin in rats with aminonucleoside nephrosis

Abstract

Micropuncture study of tubular transport of albumin in rats with aminonucleoside nephrosis.The concentration of albumin in proximal tubule fluid and urine of normal and amino-nucleoside nephrotic rats was measured by ultramicrodisc electrophoresis.A 200-fold increase in albumin excretion was found four days after aminonucleoside injection despite a significant reduction in inulin clearance and serum albumin concentration.Renal cortical blood flow was decreased to the same extent as glomerular filtration rate (GFR).Proteinuria did not relate to arterial, renal venous, or proximal tubule hydrostatic pressure which remained unchanged, and, since GFR was significantly reduced, probably was not due to an increase in glomerular capillary pressure.The concentration of albumin in glomerular filtrate of normal rats was estimated to be 0.3mg/100ml and that in animals with aminonucleoside-induced proteinuria was 2.7mg/100ml.The value in normal rats may well have been artifactually high due to trace covert contamination with serum albumin.The concentration of albumin in glomerular filtrate of the proteinuric rats calculated from the urine albumin concentration and plasma:urine 14 C-inulin activity ratio was 2.6mg/100ml, suggesting that relatively little of the filtered albumin was absorbed in transit along the nephron.Despite an estimated 30% decrease in colloid oncotic pressure of peritubular capillary blood, fractional water absorption of the nephrotic rats was no different from that of controls.It appears, therefore, that in aminonucleoside-induced nephrotic animals, at least, alterations in colloid oncotic pressure of the degree obtained in these experiments are not important to the regulation of proximal tubule fractional water absorption.