Effect of saline expansion on peritubule capillary pressures and reabsorption

The effect of extracellular volume expansion on transcapillary Starling forces, capillary uptake, and the reabsorption coefficient in the peritubule microcirculation of the dog kidney was examined. Micropuncture techniques were used to obtain measurement before and after 4% body wt expansion with isotonic saline. Extracellular volume expansion significantly changed all Starling pressures and capillary uptake. Efferent arteriolar oncotic pressure, interstitial oncotic pressure, and capillary uptake decreased (33.1 +/- 3.3 to 22.1 +/- 4.1 mmHg; 5.2 +/- 0.4 to 4.0 +/- 0.3 mmHg; and 44.9 +/- 9.2 to 28.7 +/- 8.6 nl/min, respectively), whereas capillary hydrostatic pressure and interstitial hydrostatic pressure increased (11.3 +/- 1.2 to 13.7 +/- 1.4 and 5.9 +/- 1.0 to 10.4 +/- 1.2 mmHg, respectively). The calculated reabsorption coefficient was 2.40 during hydropenia and 2.36 nl . min-1 . mmHg-1 following volume expansion. The results show that extracellular volume expansion significantly depresses capillary uptake in the dog and suggest that the decreased uptake can be accounted for totally by changes in transcapillary pressures and a constant reabsorption coefficient.