Renal function and electrolyte metabolism in acute glomerulonephritis

Differences in proximal tubular solute clearance across common etiologies of chronic kidney disease

BACKGROUND

Laboratory measures of glomerular function such as the glomerular filtration rate (GFR) contribute toward clinical evaluation of chronic kidney disease (CKD). However, diverse CKD etiologies have distinct pathological mechanisms that may differentially impact the kidney tubules. Little is known regarding how tubular function changes with varying kidney disease types.

METHODS

We used targeted mass spectrometry to quantify paired serum and urine concentration of 11 solutes of proximal tubular secretion in 223 patients from an outpatient CKD cohort. We reviewed clinic notes to ascertain the primary CKD diagnosis and categorized these as vascular, diabetic, glomerular or tubulointerstitial. We used one-way analysis of variance to compare secretory solute clearance across diagnoses setting a false discovery threshold of ≤5% and used linear regression to compare differences after adjustments for estimated GFR, age, race, sex, body mass index and urine albumin excretion.

RESULTS

After full adjustment, glomerular disease was associated with higher clearances of three tubular secretory solutes compared with vascular disease: 48% higher isovalerylglycine clearance [95% confidence interval (CI) 18-87%], 28% higher kynurenic acid clearance (95% CI 3-59%) and 33% higher tiglylglycine clearance (95% CI 7-67%). Diabetic kidney disease (DKD) was associated with 39% higher isovalerylglycine clearance compared with vascular disease (95% CI 13-72%).

CONCLUSION

Glomerular disorders and DKD are associated with higher net clearances of several secretory solutes compared with vascular causes of kidney disease. These findings suggest that different underlying etiologies of CKD may differentially impact proximal tubular secretory pathways.

The renal transport of hippurate and protein-bound solutes

Measurement of the concentration of hippurate in the inferior vena cava and renal blood samples performed in 13 subjects with normal or near-normal serum creatinine concentrations confirmed the prediction that endogenous hippurate was cleared on a single pass through the kidney with the same avidity as that reported for infused para-amino hippurate. This suggests that a timed urine collection without infusion would provide a measure of effective renal plasma flow. Comparison of the arteriovenous concentration differences for a panel of protein-bound solutes identified solutes that were secreted by the renal tubule and solutes that were subjected to tubular reabsorption.

Renal functional changes in acute glomerulonephritis in children. A one-year follow-up

Renal function was studied in three patients with post-streptococcal, four patients with IgA and one patient with non-streptococcal proliferative glomerulonephritis (GN) at the onset of the disease and two, six and 12 months later. Renal biopsies were performed at the onset of the disease and 12 months later. Standard clearance techniques were used for the functional studies. The latter were performed during hydropenia and continuous isotonic saline infusion. During hydropenia, the GFR was uniformly depressed shortly after the onset of the disease, but it normalized during the following two months. The filtration fraction was depressed in poststreptococcal GN at the onset and it normalized with the GFR. In IgA GN, the filtration fraction remained within normal limits during the entire course of the illness. The natriuretic response to isotonic saline volume expansion was low in all patients at the onset of the disease, but normalized in post-streptococcal and IgA GN during the one-year follow-up. In spite of normalized renal function, biopsy findings in IgA GN were unchanged 12 months later. An episode of macroscopic hematuria in one patient with IgA GN at the six-month investigation had no apparent effect on renal function.

Acute effects of antiglomerular basement membrane antibody on the process of glomerular filtration in the rat

Nehron filtration rate (sngfr) and the factors controlling filtration were examined before and with 60 min of the intravenous infusion of 225-450 mug of antiglomerular basement membrane antibody (AGBM Ab) (greater than 50% antigenic saturation) in plasma-expanded (2.5% body wt) Munich-Wistar rats. Pressures in glomerular capillaries (PG) and bowman's space (Pt) were measured with a servo-nulling device, systemic (piA) and efferent arteriolar oncotic pressures (piE) were measured by microprotein methods, and nephron plasma flow (rpf) and sngfr were measured by micropuncture techniques in both control and post-AGBM Ab conditions in each rat. The sngfr fell from 52.7+/-2.9 to 24.1+/-1.9 nl/min per g kidney wt (n = 7, P less than 0.001). Both afferent and efferent arteriolar resistances increased and rpf fell from 221+/-25 to 90+/-9 nl/min per g kidney wt (P less than 0.001) but the hydrostatic pressure gradient across the glomerular membrane deltaP = PG - Pt) increased from 37+/- 1 to 50+/-2 mm Hg (P less than 0.001). The increase in deltaP and a numerical decrease in piA both acted to maintain sngfr after AGBM Ab and effectively nullified the influence of decreased rpf upon sngfr. The mean effective filtration pressure (EFP = deltaP - pi) increased from 14+/-2 to 30+/-3 mm Hg (P less than 0.001) while sngfr decreased. The major and critical reason for this reduction in sngfr was a decrease in the glomerular permeability coefficient from 0.077+/-0.017 to 0.014+/-0.001 nl/s per g kidney wt per mm Hg P less than 0.001) where sngfr=EFP-LpA.

Functional adaptation of nephrons in dogs with acute progressing to chronic experimental glomerulonephritis

Although a diminished fractional excretion of sodium (FENa) is the hallmark of acute proliferative glomerulonephritis (APGN), an enhanced natriuresis per glomerular filtration rate (GFR) in the chronic phases of this disease has been reported. We studied this adaptive response utilizing two different split-bladder dog models with unilateral, and a third group of dogs with bilateral Masugi's nephritis. Group I. Six dogs with unilateral nonaccelerated APGN studied a mean of 6 days after induction had a mean base-line APGN/intact kidney GFR of 31/50 ml/min (P less than 0.005) and FENa of 0.2/0.75% (P less than 0.005). Acute volume expansion caused a smaller absolute increase in FENa from the APGN kidney, 1.6%, than from the intact kidney, 4.0%, (P less than 0.01). Maximum tubular secretion of rho-aminohippuric acid/GFR (TmPAH/GFR) measured in three dogs was higher in the APGN kidney than intact kidney, 13.1 vs. 9.3 mg/dl. Subsequent studies on three of the six dogs when the disease had become chronic demonstrated a reversal in the pattern of sodium excretion in response to volume expansion. Group II. Six dogs with accelerated unilateral APGN (dogs presensitized to antibody source) studied a mean of 5 days after induction had a mean base-line APGN/intact kidney GFR of 16/57 ml/min and FENa of 0.22/0.12% (P less than 0.1). Contrary to group I, volume expansion caused a greater absolute increase in FENa from the APGN kidney, 5.8%, than from the intact kidney, 2.9% (P less than 0.05). TmPAH/GFR studied in four dogs was similar for both kidneys, 17.9 and 18.5 mg/dl for the APGN kidney and intact kidney, respectively. Group III. Sequential studies were performed on seven dogs with bilateral nonaccelerated APGN. Initially each demonstrated sodium retention and a smaller absolute increase in FENa in response to volume expansion compared to a predisease control study. With disease progression, volume expansion induced a greater absolute increase in FENa than in the control study. We concluded that (a) the fractional excretion of sodium from the APGN kidney will be less or greater than the contralateral intact kidney or control study depending on the severity and/or chronicity of the disease, possibly as the result of morphologic alterations; (b) the degree of extracellular fluid volume expansion is an important variable influencing similarity of glomerulotubular balance between the APGN and contralateral intact kidney; and (c) the "intact nephron hypothesis" applies in a limited fashion to kidneys with APGN in the absence of volume expansion just as it does for kidneys with chronic glomerulonephritis or pyelonephritis.