Effect of volume expansion on tubular reabsorption of protein by normal and nephrotic rats.
1. Normal (N) and nephrotic (NS) rats were infused with hyperoncotic human serum albumin or isotonic saline to alter plasma albumin concentration. The renal handling of albumin was evaluated by measuring the albumin/inulin clearance ratio (CA/CIN). The dextran/inulin clearance ratio, CD/CIN, was determined using dextran of 16,000 (14C) and 70,000 (3H) molecular weight. Five groups of rats were studied: NaA, NaS, NSaA, NdS and NSdS. The subscripts A and S indicate albumin and saline infusion; the superscripts a and d denote the measurement of CA/CIN and CD/CIN. 2. When vascular volume was expanded by infusion of albumin or saline, diuresis was increased in all groups (P less than 0.05). Inulin clearance was increased (P less than 0.05) in all groups except NaS, for which it was unchanged. The CA/CIN ratio was increased (P less than 0.05) for the three groups measured, NaA, NaS, and NSaA and the increase was independent of changes in plasma albumin concentration. In contrast, C16D/CIN decreased for NdS and NSdS and C70D/CIN decreased for NSdS but was unchanged for the NdS group. 3. The increase of CA/CIN could not be correlated with high albumin load, since it was also observed when plasma albumin was lowered by saline infusion. CD/CIN did not increase with saline infusion. Therefore an increase in glomerular permeability due to the volume expansion could not explain the increase in CA/CIN during albumin infusion. 4. We conclude that the depression of albumin reabsorption was a consequence of volume expansion. A model is presented which accounts for the effect of increased tubular flow on albumin reabsorption.
D000818:Animals; D003911:Dextrans / Q000378:metabolism*; D005919:Glomerular Filtration Rate; D006400:Hematocrit; D007552:Isotonic Solutions / Q000378:metabolism; D007684:Kidney Tubules / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D009404:Nephrotic Syndrome / Q000378:metabolism* / Q000503:physiopathology; D051381:Rats; D012709:Serum Albumin / Q000378:metabolism*
D003911:Dextrans; D007552:Isotonic Solutions; D012709:Serum Albumin