Postglomerular Control of Fluid Reabsorption by the Renal Proximal Tubule1

The Na/H exchanger isoform 3 (NHE3) is expressed in the proximal tubule and thick ascending limb and contributes to the reabsorption of fluid and electrolytes in these segments. The contribution of NHE3 to fluid reabsorption was assessed by micropuncture in homozygous ( Nhe3 −/−) and heterozygous ( Nhe3 +/−) knockout mice, and in their wild-type (WT, Nhe3 +/+) littermates. Arterial pressure was lower in the Nhe3 −/−mice (89 ± 6 mmHg) compared with Nhe3 +/+ (118 ± 4) and Nhe3 +/−(108 ± 5). Collections from proximal and distal tubules demonstrated that proximal fluid reabsorption was blunted in both Nhe3 +/− and Nhe3 −/−mice (WT, 4.2 ± 0.3; Nhe3 +/−, 3.4 ± 0.2; and Nhe3 −/−, 2.6 ± 0.3 nl/min; P < 0.05). However, distal delivery of fluid was not different among the three groups of mice (WT, 3.3 ± 0.4 nl/min; Nhe3 +/−, 3.3 ± 0.2 nl/min; and Nhe3 −/−, 3.0 ± 0.4 nl/min; P < 0.05). In Nhe3 −/−mice, this compensation was largely attributable to decreased single-nephron glomerular filtration rate (SNGFR): 10.7 ± 0.9 nl/min in the Nhe3 +/+ vs. 6.6 ± 0.8 nl/min in the Nhe3 −/−, measured distally. Proximal-distal SNGFR differences in Nhe3 −/−mice indicated that much of the decrease in SNGFR was due to activation of tubuloglomerular feedback (TGF), and measurements of stop-flow pressure confirmed that TGF is intact in Nhe3 −/−animals. In contrast to Nhe3 −/−mice, normalization of early distal flow rate in Nhe3 +/−mice was not related to decreased SNGFR (9.9 ± 0.7 nl/min), but rather, to increased fluid reabsorption in the loop segment ( Nhe3 +/+, 2.6 ± 0.2; Nhe3 +/−, 3.6 ± 0.5 nl/min). We conclude that NHE3 is a major Na/H exchanger isoform mediating Na+ and fluid reabsorption in the proximal tubule. In animals with NHE3 deficiency, normalization of fluid delivery to the distal tubule is achieved through alterations in filtration rate and/or downstream transport processes.

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Astrogliosis inhibition attenuates hydrocephalus by increasing cerebrospinal fluid reabsorption through the glymphatic system after germinal matrix hemorrhage

Experimental Neurology ◽

10.1016/j.expneurol.2019.113003 ◽

2019 ◽

Vol 320 ◽

pp. 113003 ◽

Cited By ~ 8

Author(s):

Yan Ding ◽

Tongyu Zhang ◽

Guangyong Wu ◽

Devin W. McBride ◽

Ningbo Xu ◽

...

Keyword(s):

Cerebrospinal Fluid ◽

Germinal Matrix ◽

Fluid Reabsorption ◽

Glymphatic System ◽

Germinal Matrix Hemorrhage

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Role of luminal hydrostatic pressure in proximal tubular fluid reabsorption in the rat

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1975.229.3.813 ◽

1975 ◽

Vol 229 (3) ◽

pp. 813-819 ◽

Cited By ~ 2

Author(s):

A Grandchamp ◽

Scherrer ◽

D Scholer ◽

J Bornand

Keyword(s):

Hydrostatic Pressure ◽

Proximal Tubule ◽

Pressure Difference ◽

Unit Area ◽

Rat Kidney ◽

Fluid Reabsorption ◽

Proximal Tubular ◽

Tubular Fluid Reabsorption ◽

Selective Change

The effect of small changes in intraluminal hydrostatic pressure (P) on the tubular radius (r) and the net fluid reabsorption per unit of surface area of the tubular wall (Js) has been studied in the proximal tubule of the rat kidney. The split-drop method was used to simultaneously determine Js and r. Two standardized split-drop techniques A and B allow selective change in P. P was 31.6 +/- 1.3 mmHg in technique A and 15.5 +/- 1.5 in technique B. The pressure difference significantly affected the tubular radius; r was 21.9 +/- 0.4 and 18.6 +/- 0.5 mum in the split drop A and B, respectively. In contrast, net transepithelial fluid reabsorption Js was unchanged. Js amounted to 2.72 +/- 0.20, and 2.78 +/- 0.33 10(-5) cm3 cm-2 s-1 in split drop A and B. The absence of variations in Js could result from two opposite effects of pressure. P might enhance Js by increased ultrafiltration. However, the rise in r might decrease the density of the intraepithelial transport paths per unit area of tubular wall and therefore might decrease Js.

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Renal cortical interstitium and fluid absorption by peritubular capillaries

AJP Renal Physiology ◽

10.1152/ajprenal.1994.266.2.f175 ◽

1994 ◽

Vol 266 (2) ◽

pp. F175-F184 ◽

Cited By ~ 6

Author(s):

K. Aukland ◽

R. T. Bogusky ◽

E. M. Renkin

Keyword(s):

Rat Kidney ◽

Colloid Osmotic Pressure ◽

Capillary Wall ◽

Peritubular Capillary ◽

Fluid Reabsorption ◽

Fluid Uptake ◽

Peritubular Capillaries ◽

Capillary Fluid ◽

Renal Cortical Interstitium ◽

Relative Retardation

Every minute, the cortical peritubular capillaries in a 1-g rat kidney take up more than 0.5 ml tubular reabsorbate. Studies of renal lymph and measurements of pressure in capillaries (Pc) and interstitium (Pi) indicate that normally the protein colloid osmotic pressure of peritubular capillary plasma (COPp) provides the necessary absorptive force, keeping Pi at 2-4 mmHg, i.e., 8-10 mmHg lower than Pc. At reduced COPp, continued delivery of fluid from the tubules automatically raises Pi to maintain capillary fluid uptake. The transient Pi response to sudden exposure of the kidney to subatmospheric pressure shows that such adjustment of forces may take place in only 5 s. Most remarkable, adjustment of forces may take place in only 5 s. Most remarkable, reabsorption continues during protein-free perfusion of the isolated rat kidney, apparently effected by a Pi exceeding Pc. A relative retardation of interstitial uptake of ferritin from plasma in this case suggests fluid reabsorption through both small and large pores in the capillary wall. Collapse of the capillaries is presumably prevented by tight tethering to the capillary wall, giving the narrow interstitium a very low compliance.

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