Mechanism of Inhibition of Proximal Tubule Fluid Reabsorption after Exposure of the Rat Kidney to the Physical Effects of Expansion of Extracellular Fluid Volume
AUTOR(ES)
Ichikawa, Iekuni
RESUMO
The natriuresis and concomitant decline in absolute proximal reabsorption (APR) that occur in rats in response to saline loading are blunted markedly when renal perfusion pressure is reduced immediately before, but not after, the volume load. To ascertain the mechanism responsible for these differences between early clamp (EC) vs. late clamp (LC), intracapillary and interstitial determinants of peritubular capillary uptake of APR were measured in seven LC and seven EC Munich-Wistar rats before and after isotonic saline loading (80% body wt). With volume expansion in LC animals, we observed a marked decline in APR (averaging 11±1 nl/min), associated with large increases in urinary sodium excretion rate, which averaged 8±2 μeq/min. In EC, the changes in urinary sodium excretion rate (+1±0 μeq/min) and APR (−3±1 nl/min) with volume expansion were smaller in magnitude. Since peritubular capillary reabsorption coefficient and mean peritubular transcapillary hydraulic pressure difference did not change with saline loading in LC, the marked fall in APR was attributed primarily to a measured large decline in mean peritubular transcapillary oncotic pressure difference (δ̄π̄). Despite an equivalent mean fall in δ̄π̄ with volume expansion in EC, near-constancy of APR was found to be associated with a simultaneous and equivalent decline in mean peritubular transcapillary hydraulic pressure difference (a consequence of decreased mean peritubular capillary hydraulic pressure), which effectively offset the fall in δ̄π̄. These results demonstrate the importance of hydraulic pressure patterns of the peritubular capillaries in modulating APR and are consistent with the view that Starling forces across the postglomerular microcirculation play a fundamental role in determining APR.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=371296Documentos Relacionados
- On the Mechanism of Inhibition in Fluid Reabsorption by the Renal Proximal Tubule of the Volume-Expanded Rat
- Dependence of Saline-Induced Natriuresis upon Exposure of the Kidney to the Physical Effects of Extracellular Fluid Volume Expansion
- On the influence of extracellular fluid volume expansion on bicarbonate reabsorption in the rat
- Mechanism of NaCl and water reabsorption in the proximal convoluted tubule of rat kidney.
- The effects of anions on fluid reabsorption from the proximal convoluted tubule of the rat.