Effect of renal venous pressure elevation on tubular sodium and water reabsorption in the dog kidney

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Abstract
This study was performed in order to quantify the effects of renal venous pressure (RVP) elevation on absolute and fractional reabsorption rates of sodium and water in proximal and distal segments of the nephron in dog kidneys. Renal blood flow (RBF) was measured electromagnetically. Clearance of [51Cr]EDTA was used as a measure of the rate of glomerular filtration (GFR). GFR, urinary excretion rates of sodium and water, and lithium clearance were used for assessing the absolute and fractional reabsorption rates of sodium and water in the proximal as well as in more distal segments of the nephron. In the kidneys with intact innervation RVP elevation to 19.9±0.1 mmllg caused significant increases in both absolute (APR) and fractional (FPR) proximal reabsorption rates from 33.4 ± 4.2 to 38.7 ± 2.0 ml min and from 0.62 ± 0.04 to 0.71 ± 0.04, respectively. These responses were unaffected by acute surgical denervation of the kidneys. In contrast, chronic renal denervation or infusion of phentolamine (5 μg kg‐1min‐1) into the renal artery eliminated the increase in APR and FPR during RVP elevation to 20 mmHg. Chronic, but not acute renal denervation depleted renal tissue content of adrenaline and noradrenaline. The results suggest that the increase in APR and FPR during RVP elevation is due mainly to local sympathetic reflex mechanisms.