Increased ureteral back pressure enhances renal tubular sodium reabsorption

Abstract

A B S T R A C T Moderate increases of ureteral back pressure usually cause decreases of glomerular filtration rate and even greater decreases of sodium excretion. It has been assumed previously that increased ureteral back pressure does not enhance renal tubular sodium reabsorption directly and that the decreases of sodium excretion are caused by the decreases of glomerular filtration rate. In the experiments reported here, the effect of increased ureteral back pressure on urinary-sodium excretion was studied in dogs in which changes of filtration rate were minimized by infusing saline while ureteral back-pressure was increased.When ureteral back pressure was increased on one side by 10-23 cm of water, the inulin clearance of the experimental kidney decreased by only 3-12% in 21 experiments, did not change significantly (±2%) in eight experiments, and increased by 3-8% in seven experiments. The sodium excretion of the experimental kidney decreased in al experiments regardless of whether its inulin clearance increased, decreased, or was unchanged from control values.When the inulin clearance of the experimental kidney increased or remained unchanged during increased ureteral back pressure, its reabsorption of sodium increased more than could be accounted for by the increase of filtered sodium. When the inulin clearance of the experimental kidney decreased during increased ureteral back pressure, its reabsorption of sodium decreased less than could be accounted for by the decrease of filtered sodium.Therefore, the effect of increased ureteral back pressure to decrease urinary sodium excretion is caused in part by increased tubular reabsorption of sodium.

Influence of Intrapelvic Pressure on Excretion of Sodium from Human Hydronephrotic Kidneys

“…A reduced sodium concentration in urine from the obstructed kidney has also been demonstrated [Suki et al, 1966[Suki et al, , 1971]. This decrease in sodium excretion is not entirely due to reduced GFR and thereby a decrease in sodium load on renal tubules, but also to increased tubu lar sodium resorption [Share, 1952;Suki et al, 1966Suki et al, , 1971Fulop and Brazeau, 1970]. On the other hand, chronic ureteral obstruction leads to increased fractional The present study concerns sodium excretion, urinary flow, and intrapelvic pressure in 12 obstructed kidneys studied during basal conditions and during Mannitolinduced diuresis.…”

“…The amount of sodium excreted from obstructed kid neys during Mannitol infusion was negatively correlated to the maximum intrapelvic pressure (r = 0.9110; p < The influence of ureteric obstruction on sodium excre tion in animals has previously been studied [Selkurt et al, 1952;Share, 1952;Suki et al, 1966Suki et al, , 1971Fulop and Brazeau, 1970], and a decrease in sodium excretion after acute moderate increase of intrapelvic pressure has been found. A reduced sodium concentration in urine from the obstructed kidney has also been demonstrated [Suki et al, 1966[Suki et al, , 1971].…”

The Relation between the Urinary Excretion of Inorganic Phosphate and Sodium

“…We have shown that under those conditions UNaV decreases even when GFR remains stable or increases slightly during increased ureteral backpressure (Fulop & Brazeau, 1970). The decreased UNaV in the presence of a constant or increased filtered load of sodium (F Na) was, therefore, attributed to increased T Na (Fulop & Brazeau, 1970). Urinary P excretion was measured in twenty-four of those experiments and the results are reported here.…”

“…Lesser increases of ureteral backpressure in dogs given saline infusions may be attended by little change of GFR or even modest increases, because the GFR-depressing effect of ureteral pressure elevation is off-set by the GFR-enhancing effect of saline infusion. We have shown that under those conditions UNaV decreases even when GFR remains stable or increases slightly during increased ureteral backpressure (Fulop & Brazeau, 1970). The decreased UNaV in the presence of a constant or increased filtered load of sodium (F Na) was, therefore, attributed to increased T Na (Fulop & Brazeau, 1970).…”

Partial unilateral ureteral obstruction in rats

“…As a result of PUUO, GFR may increase, remain unchanged, or decrease, depending on the duration, severity of obstruction, and diuretic state [Fulop and Brazeau, 1970;Navar and Baer, 1970;Suki et al, 1971;Groshar et al, 1996]. In general, ureteral obstruction results in decreased renal blood £ow (RBF) and GFR in the ipsilateral kidney and increased RBF to the intact opposite kidney [Josephson, 1991;Wen et al, 1999a].…”