Effects of extracellular volume expansion on the tubular reabsorption of glucose

Abstract

Clearance and intratubular injections of (¹⁴C) glucose were performed in glucose loaded rats, during control (C) and extracellular fluid volume expansion (VE) to 10% of body weight. VE resulted in a significant decrease in hematocrit from 47.50±1.06 to 38.80±1.14% and plasma protein from 6.23±0.25 to 4.13±0.21 gm/100ml. Glomerular filtration rate (GFR) increased by 51% from 1.06±0.07 to 1.60±0.35 ml/min. Fractional excretion of sodium increased significantly from 0.42±0.07 to 12.58±1.25%. Maximal glucose reabsorption (TmG) was unchanged from 3.47±0.42 to 3.29±0.41 mg/min. However, TmG/GFR decreased significantly from 3.14±0.22 to 1.94±0.21 mg/ml GFR. As compared to C, VE resulted in a significant increase in (¹⁴C) glucose recovery after injection into the early and late proximal tubules, from 63±3 to 81±2% and 82±2 to 88±1% respectively. After distal tubular injections (¹⁴C) glucose recovery was complete in both C and VE; early distal injection 97±1 vs 98±1%, late distal injection 98±1 vs 99±1%. These results indicate an inhibitory effect of VE on fractional glucose reabsorption in the superficial nephron. There is no evidence for glucose reabsorption in the superficial distal nephron during C and VE.