ExtractThe relationship between glomerular filtration rate and proximal tubular fluid reabsorption was evaluated in control rats and in rats 96 and 144 hr after the injection of an aminonucleoside of puromycin. Urine volume and sodium excretion were decreased in the rats injected with aminonucleoside. Proteinuria increased progressively. Total kidney glomerular filtration rate (GFR) was diminished less than surface nephron GFR at 96 hr and greater than single nephron GFR at 144 hr after injection when a large proportion of nephrons are nonfunctional. Clearance ofp-aminohippurate was unchanged initially and depressed subsequently after aminonucleoside injection. Absolute reabsorption to the end of the proximal convolution was unaltered despite a decrease in total kidney filtration fraction. This decrease in GFR coupled with unchanged absolute reabsorption and hence increased fractional proximal reabsorption leads to decreased delivery of sodium and fluid to the more distal portions of the nephron.SpeculationGlomerular filtration rate is decreased in rats with aminonucleoside nephrosis. Absolute reabsorption along the proximal tubule is not reduced proportionally. The increase in fractional reabsorption which results coupled with a decrease in GFR may be an important source of fluid and sodium retention and thus edema formation in this disease.