The relationship between glomerular filtration rate and sodium reabsorption by the proximal tubule of the rat nephron

Abstract

We have tested two of the hypotheses proposed to explain the adjustment in sodium reabsorption in the proximal tubule that follows a change in the rate of glomerular filtration (glomerulotubular balance). Using the recollection micropuncture technique, we were able to measure the immediate and late changes in reabsorptive rate after an acute alteration in filtration rate produced by aortic constriction and release of constriction. It was found that fractional reabsorption, as measured by the inulin tubule fluid to plasma (TF/P) ratio, increased after aortic constriction and decreased after release, but that in most instances, absolute reabsorptive rate changed in parallel to glomerular filtration rate. The change was similar whether the collections were made less than 1 or more than 5 min after the change in blood pressure. dence against an intrarenal humoral feedback mechanism.In the same experiments we measured the (TF/P) ,, transit time, and flow rate of fluid in single nephrons before and during aortic constriction or release of aortic constriction. The change in reabsorptive rate and the simultaneous change in calculated cross-sectional area of the tubule lumen were rarely proportional, i.e., C/irr2 was not constant. In other experiments, these same measurements were made before and during periods of increased ureteral pressure. Despite large increments in calculated cross-sectional area, the absolute rate of reabsorption either remained relatively unchanged or fell in proportion to the change in filtration rate. It is concluded that under these conditions, reabsorptive rate is. governed by some factor other than tubule geometry.

An inhibitory effect of furosemide on sodium reabsorption by the proximal tubule of the rat nephron

“…Water was available ad lib. They were anesthetized with Inactin (100 mg/kg), placed on a heated micropuncture table, and prepared for study in a manner previously described (11). Indwelling polyethylene catheters were placed in the left jugular vein for infusion of inulin and furosemide, into the right jugular vein for injection of Lissamine green, and into the left femoral artery for periodic sampling of blood and measurement of arterial pressure.…”

“…In a recent micropuncture study of the effect of elevated ureteral pressure on fractional sodium reabsorption by the proximal tubule in the rat ( 11), it was found that unless special care was taken to prevent retrograde flow of tubule fluid from more distal sites, the calculated value for fractional sodium reabsorption was elevated spuriously. This artifact results from the collection of fluid from more distal sites along the nephron where, as a result of continued water reabsorption, the inulin concentration is higher.…”

Effect of Endothelin-3(ET-3) on Renal Function in Rat Perfused Kidney.

“…It is possible therefore that a lower dose of ET-3 may elicit intrarenal vasodilation without affecting the overall renal vascular resistance, which results in an increase in GFR. The observed increase in FENa induced by a high dose of ET-3 might have reflected the glomerulotubular balance to some degree [ 12]. However, we consider that the pressure natriuresis which is thought to be caused by the increase in the hydraulic pressure in a peritubular capillary in consequence of the high perfusion pressure following the infusion of a high dose of ET-3 mainly increase the FENa, since there was no change in the perfusion pressure and FENa after infusion of the vehicle or a low dose of ET-3.…”

Effect of saline infusions on intrarenal distribution of glomerular filtrate and proximal reabsorption in the dog

“…Dirks, Cirksena, and Berliner (3) found in the dog that fractional reabsorption was suppressed after volume expansion, and that this reduction persisted when filtration rate was lowered below hydropenic levels by arterial clamping. Other investigators, however, have found that fractional reabsorption during saline diuresis tends to return toward hydropenic levels after aortic constriction in the rat (16)(17)(18). Second, the change in total GFR is not of a sufficient magnitude to explain the change in fractional reabsorption (3,15).…”