Proximal tubular injury attenuates outer medullary hypoxic damage: studies in perfused rat kidneys

The straight segment (S3) of the proximal tubule is predominantly damaged during renal ischemia-reflow, whereas medullary thick ascending limbs (mTALs) are principally affected in other models of hypoxic acute tubular necrosis (ATN). Since the latter injury pattern largely depends on the extent of reabsorptive activity during hypoxic stress, we hypothesized that proximal tubular damage might attenuate downstream mTAL injury by means of diminished distal solute delivery for reabsorption. In isolated rat kidneys perfused for 90 min with oxygenated Krebs-Henseleit solution, mTAL necrosis developed in 75 +/- 3% of tubules in the mid-inner stripe of the outer medulla. By contrast, S3 segments in the outer stripe were minimally affected, with tubular fragmentation involving some 5 +/- 2% of tubules. In kidneys subjected in vivo to proximal tubular injury and subsequently used for isolated perfusion studies, the injury pattern was inverted: following 20 and 30 min ischemia and reflow for 24 h, S3 fragmentation rose to 18 +/- 16% and 72 +/- 13%, while mTAL damage was reduced to 33 +/- 10 and 24 +/- 8%, respectively. In kidneys subjected in vivo to D-serine S3 necrosis rose to 100%, while mTAL damage fell to 1 +/- 1% (p < 0.001). Substantial S3 tubular collapse (involving approximately 30% of tubules) and inner stripe interstitial hemorrhage were also noted, exclusively in kidneys subjected to ischemia-reflow. Proximal tubular necrosis alone or in combination with collapse inversely correlated with mTAL necrosis (R = -0.51 and -0.72, respectively, p < 0.003). This cogent inverse association might imply that disruption of the proximal nephron attenuates downstream mTAL necrosis by a reduction of distal tubular reabsorptive workload.     

Role of the loop segment in the urinary concentrating defect of hypercalcemia

Hypercalcemia is associated with impaired urinary concentrating ability. To explore the mechanism(s) by which hypercalcemia impairs chloride transport in the loop of Henle, we carried out in vivo microperfusion of the loop segment in Sprague-Dawley rats rendered acutely hypercalcemic (12.1 +/- 0.1 mg/dliter) by calcium gluconate infusion. Control rats were infused with sodium gluconate and had normal plasma calcium (8.0 +/- 0.2 mg/dliter). Compared to control, fractional chloride reabsorption was decreased (61 +/- 4 to 50 +/- 3%; P less than 0.05) and early distal chloride increased 74 +/- 6 to 98 +/- 3 mEq/liter (P less than 0.001) in hypercalcemia. During hypercalcemia, infusion of verapamil failed to increase fractional chloride reabsorption (49 +/- 4%; P less than 0.05) or decrease early distal chloride (95 +/- 2; P less than 0.05) toward control values. Similarly, indomethacin did not improve fractional chloride reabsorption (48 +/- 4%; P less than 0.05) or distal chloride concentration (93 +/- 7; P less than 0.05). In control rats infused with Ringers HCO3, the addition of calcium 8.0 mEq/liter to the perfusate increased early distal calcium (9.22 to 3.11 mEq/liter) but was associated with no change in fractional chloride reabsorption (-6 +/- 6%) and a slight decrease in early distal chloride (-9 +/- 3 mEq/liter; P less than 0.05). These data are consistent with the hypothesis that an elevated plasma, not luminal calcium, concentration impairs chloride reabsorption in the loop segment, primarily the ADH-stimulated component. This may have an important role in the urinary concentrating defect of hypercalcemia.     

On the probability that kidneys are different in autosomal dominant polycystic disease.

We hypothesized that highly variable cyst fluid sodium concentrations are a characteristic of every kidney in autosomal dominant polycystic kidney disease (ADPKD). We added our data on sodium concentrations in 124 fluids from ten ADPKD kidneys to data published by others of concentrations in 32 fluids from five kidneys. The values ranged from 3 to 207 mEq/liter; none fell between 59 and 74 mEq/liter. Fluids were designated as low (< 60 mEq/liter; 50 fluids) or high (> 60 mEq/liter; 106 fluids) sodium fluids. Transmission electron microscopy identified differences in the depths of apical tight junctions between cells from cyst walls of 12 of the low and 10 of the high sodium fluids from two kidneys (mean +/- SE depths of 2039 +/- 74 A vs. 386 +/- 18 A respectively; P < 0.0001). When fluids were grouped by kidney of origin, six of the 15 kidneys had only high sodium fluids. The probability that chance had led to the sampling of only high sodium fluids in these organs, given that 32% of all fluids were low sodium fluids, was calculated at < 0.00015. The possibility must be considered that all kidneys are not alike in ADPKD.     

Some aspects of proximal tubular sodium chloride reabsorption in Necturus kidney.

Some aspects of proximal tubular sodium chloride reabsorption in Necturus kidney. Renal tubular reabsorption of fluid and sodium was measured by clearance methods in the doubly perfused Necturus kidney in which the bicarbonate concentration was varied between 0 and 60 mEq/liter. The effects of Damox (2.2 times 10-3M), ocubain (10-5M) and ethacrynic acid (10-4M) and of acidosis were also investigated. In addition to clearance experiments, stationary microperfusion experiments were carried out on promimal tubules to measure volume flow and steady-state sodium and chloride concentration differences across the tubular epithelium. In some experiments, the transepithelial electrical potential difference was also measured using an axial electrode system. The following results were obtained: 1) Bicarbonate is not essential to the operation of renal tubular fluid and sodium transport. 2) Total renal and proximal tubular fluid and sodium transport are partially inhibited by Diamox, ouabian and ethacrynic acid. 3) The proximal tubule maintains a significant transepithelial sodium and chloride concentration difference and a significant electrical potential difference (lumen-negative) in the presence of a poorly permeant nonelectrolyte. The direction and magnitude of the electrical polarization fully accounts for the observed chloride concentration difference. The data support the thesis that sodium chloride transport accross the proximal tubular epithelium takes place by active sodium transport and electically coupled passive chloride reabsorption. Important species differences with respect to mammalian transport mechanisms are discussed.     

Dietary NaCl determines severity of potassium depletion-induced metabolic alkalosis

It is uncertain whether, in humans, potassium depletion can cause or sustain metabolic alkalosis of clinically important degree in the absence of coexisting known alkalosis-producing conditions. Previously we found, in normal humans ingesting abundant NaCl, that dietary K+ depletion alone can induce and sustain a small decrease in blood acidity and increase in plasma bicarbonate concentration; we hypothesized that more severe alkalosis was prevented by mitigating mechanisms initiated by renal retention of dietary NaCl that was induced by K+ depletion. To ascertain the acid-base response to dietary K+ depletion under conditions in which the availability of NaCl for retention is greatly limited, in the present study of six normal men we restricted dietary K+ as in the previous study except that intake of NaCl was maintained low (2 to 7 mEq/day, Low NaCl Group) instead of high (126 mEq/day, High NaCl Group). Plasma acid-base composition and renal net-acid excretion (NAE) did not differ significantly between groups during the control period. In the steady state of K+ depletion (days 11 to 15 of K+ restriction), neither plasma K+ concentration (2.9 +/- 0.9 mEq/liter vs. 3.0 +/- 0.1 mEq/liter) nor cumulative K+ deficit (399 +/- 59 mEq vs. 466 +/- 48 mEq) differed significantly between groups. During K+ restriction, persisting metabolic alkalosis developed in both groups, which was more severe in the Low NaCl Group: increment in [HCO3-]p, 7.5 +/- 1.0 mEq/liter versus 2.0 +/- 0.3 mEq/liter, P less than 0.001; decrement in [H+]p, 5.5 +/- 0.6 nEq/liter versus 2.9 +/- 0.4 nEq/liter, P less than 0.003. A significantly more severe alkalosis in the Low NaCl Group was evident at all degrees of K+ deficiency achieved during the course of the 15 days of K+ restriction, and the severity of alkalosis in the Low NaCl Group correlated with the degree of K+ deficiency. During the generation of alkalosis (days 1 to 7 of K+ restriction), NAE increased in the Low NaCl Group whereas it decreased in the High NaCl Group. During the maintenance of alkalosis (days 11 to 15), NAE stabilized in both groups after it returned to values approximating the control values. In both groups, urine Cl- excretion decreased during K+ restriction even though Cl- intake had not been changed, with the result that body Cl- content increased negligibly in the Low NaCl Group (28 +/- 6 mEq) and substantially in the High NaCl Group (355 +/- 64 mEq).(ABSTRACT TRUNCATED AT 400 WORDS)     

Does cyclooxygenase-2 inhibitor prevent renal tissue damage in unilateral ureteral obstruction?

PURPOSE: We determined whether the cyclooxygenase-2 inhibitor etodolac affects renal tubular damage and interstitial fibrosis in unilateral ureteral obstruction. MATERIALS AND METHODS: Etodolac (10 mg./kg.) was administered to rats 1 day before unilateral ureteral obstruction and every day thereafter. Kidneys were harvested at day 14 after unilateral ureteral obstruction. Tissue transforming growth factor-beta and prostaglandin E2 were measured by bioassay using mink lung epithelial cells and enzyme linked immunosorbent-sandwich assay. Renal tubular proliferation and apoptosis were detected by immunostaining with proliferating cellular nuclear antigen and by terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labeling, respectively. Cyclooxygenase-2 expression was detected by immunohistochemistry. Fibrosis was assessed by measuring collagen deposition in trichrome stained slides. RESULTS: Bioassay showed that in the control group obstructed kidneys contained significantly higher mean transforming growth factor-beta1 than unobstructed kidneys (79.1 +/- 8.3 versus 33.6 +/- 4.2 ng./gm. tissue) and etodolac significantly decrease the mean value in obstructed kidneys (46.2 +/- 10.0 ng./gm. tissue). Assay demonstrated that obstructed control kidneys had significantly more mean tubular apoptosis than their unobstructed counterparts (26.6 +/- 5.4 versus 2.2 +/- 1.4 nuclei per high power field) and etodolac significantly decreased mean renal tubular apoptosis in the obstructed kidneys (16.2 +/- 1.9 nuclei per high power field). In addition, immunostaining with proliferating cellular nuclear antigen showed that obstructed kidneys in the control group had significantly more mean renal tubular proliferation than unobstructed kidneys (9.8 +/- 3.4 versus 3.9 +/- 0.1 per high power field) and etodolac significantly increased mean proliferating renal tubule in the obstructed kidneys (24.9 +/- 4.3 per high power field). Control obstructed kidneys had significantly more fibrosis and prostaglandin E2 production, which were also significantly blunted by etodolac. CONCLUSIONS: The cyclooxygenase-2 inhibitor etodolac significantly reduces tissue transforming growth factor-beta, resulting in decreased tubular damage and interstitial fibrosis. This finding suggests that etodolac is a promising agent for preventing renal tissue damage in unilateral ureteral obstruction.     

Tranilast ameliorates renal tubular damage in unilateral ureteral obstruction

PURPOSE: We determined whether tranilast, the anti-allergic agent N-(3, 4-dimethoxyciannamoyl)-anthranilic acid, would diminish renal transforming growth factor-beta (TGF-beta) levels in unilateral ureteral obstruction and concomitantly affect renal tubular apoptosis and proliferation in that condition. MATERIALS AND METHODS: Tranilast (150 mg./kg.) was administered to rats 1 day before unilateral ureteral obstruction and each day thereafter. Kidneys were harvested day 14 after unilateral ureteral obstruction. Tissue TGF-beta was measured by bioassay using mink lung epithelial cells. Renal tubular proliferation and apoptosis were detected by immunostaining proliferating cell nuclear antigen and the terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labeling assay, respectively. Fibrosis was assessed by measuring collagen deposition with trichrome stained slides. RESULTS: TGF-beta bioassay showed that obstructed kidneys in controls contained significantly higher mean TGF-beta plus or minus standard deviation than unobstructed kidneys in controls (73.7 +/- 13.6 versus 14.1 +/- 5.5 pg./mg. tissue) and tranilast significantly decreased tissue TGF-beta in obstructed kidneys (15.9 +/- 4.8 pg./mg. tissue). The terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labeling assay demonstrated that obstructed kidneys in controls had significantly more mean tubular apoptosis than the unobstructed counterparts (36.6 +/- 6.7 versus 5.8 +/- 5.5 nuclei per high power field) and tranilast significantly decreased mean renal tubular apoptosis in obstructed kidneys (16.2 +/- 1.7 nuclei per high power field). In addition, immunostaining proliferating cell nuclear antigen showed that obstructed kidneys in controls had significantly more mean renal tubular proliferation than unobstructed kidneys (20.7 +/- 3.4 versus 6.2 +/- 2.1 per high power field) and tranilast significantly increased proliferating renal tubules in obstructed and unobstructed kidneys (26.5 +/- 8.3 and 14.5 +/- 3.4 per high power field, respectively). Control obstructed kidneys exhibited significantly more fibrosis, which was also blunted by tranilast. CONCLUSIONS: Tranilast significantly decreases tissue TGF-beta, resulting in a reduction in tubular apoptosis and an increase in tubular proliferation. This finding suggests that tranilast is a promising agent for preventing renal tubular damage in unilateral ureteral obstruction.     

Lithium-induced impairment of urine acidification.

The purpose of this study was to clarify the means by which lithium induced a disorder of urine acidification. Rats infused with hydrochloric acid (1 mEq/kg) developed acute metabolic acidosis (blood Ph = 7.32; bicarbonate, 18 mEq/liter) with a urine pH of approximately 5.85. The addition of lithium chloride (4 mEq/kg i.p) caused an increase in the urine pH (6.38) and a further decrease in blood bicarbonate (11.0 mEq/liter). During bicarbonate loading, lithium caused the urine PCO2 to fall significantly (urine minus blood PCO2 decreased from 25.3 +/-2.8 To 14.4 +/- 2.3 mm Hg) These changes were not seen following equimolar i.p. administration of sodium chloride. Similarly, lithium administration depressed bicarbonate reabsorption by 11.1% (from 30.6 to 27.2muEq/ml of GFR) during alkali infusion, while saline caused only a 5% decrease (30.0 to 28.5muEq/ml of GFR). The combination of an increase in urine PCO2 in alkaline urine indicates that lithium produced a defect in distal nephron hydrogen ion secretion. The fall in bicarbonate reabsorption following lithium administration oculd be due to a mild hydrogen ion secretory defect located in the proximal tubule or a severe defect in the distal nephron.     

Impaired renal acidification following acute renal ischemia in the dog

Transient renal tubular acidosis may complicate acute renal failure (ARF). To clarify this phenomenon, the present study examined tubular H+ ion secretory capacity in an ischemic model of ARF. Clearance studies were performed in dogs subjected to 60 minutes, unilateral renal artery clamping. The contralateral kidney served as control. One hour after release of clamp, mean glomerular filtration rate (GFR) was reduced by 50 to 70 percent in the ischemic kidney. Bicarbonate reclamation (mEq/liter GFR) was comparable in both kidneys. However, ischemia resulted in impaired distal acidification as judged by three separate maneuvers: minimal urinary pH following sulphate infusion was higher in ischemic than in control kidney (6.61 +/- 0.39 vs. 5.39 +/- 0.26, P less than 0.01), mean urine to blood PCO2 difference (U-B PCO2) was significantly lower during phosphate infusion (ischemic: 13.8 +/- 4.1 mm Hg, control: 37.2 +/- 6.8 mm Hg, P less than 0.01) and was completely abolished during isotonic NaHCO3 infusion in the ischemic kidney (-1.9 +/- 3.4 mm Hg) compared to control (40.1 +/- 14.8 mm Hg, P less than 0.05). Urinary potassium excretion was intact following ischemia and was appropriately suppressed by amiloride. Administration of 0.7 M NaHCO3 solution at a rate sufficient to produce maximally alkaline urine resulted in a similar U-B PCO2/UHCO3 relationship in both kidneys in the face of impaired distal acidification in the ischemic kidney. This suggests either that the defect may be reversed by massive bicarbonate infusion or, alternatively, that U-B PCO2 difference may be related to other factors in addition to distal H+ secretion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sodium-hydrogen exchanger regulatory factor-1 interacts with mouse urate transporter 1 to regulate renal proximal tubule uric acid transport

Sodium-hydrogen exchanger regulatory factor-1-deficient (NHERF-1(-/-)) mice demonstrate increases in the urinary excretion of phosphate, calcium, and uric acid associated with interstitial deposition of calcium in the papilla of the kidney. These studies examine the role of NHERF-1 in the tubular reabsorption of uric acid and regulation of mouse urate transporter 1 (mURAT1), a newly described transporter that is responsible for the renal tubular reabsorption of uric acid. In primary cultures of mouse renal proximal tubule cells, uric acid uptake was significantly lower in NHERF-1(-/-) cells compared with wild-type cells over a large range of uric acid concentrations in the media. Western immunoblotting revealed a 56 +/- 6% decrease in the brush border membrane (BBM) expression of mURAT1 in NHERF-1(-/-) compared with wild-type control kidneys (P < 0.05). Confocal microscopy confirmed the reduced apical membrane expression of mURAT1 in NHERF-1(-/-) kidneys and demonstrated mislocalization of mURAT1 to intracellular vesicular structures. Para-aminohippurate significantly inhibited uric acid uptake in wild-type cells (41 +/- 2%) compared with NHERF-1(-/-) cells (8.2 +/- 3%). Infection of NHERF-1(-/-) cells with adenovirus-green fluorescence protein-NHERF-1 resulted in significantly higher rates of uric acid transport (15.4 +/- 1.1 pmol/microg protein per 30 min) compared with null cells that were infected with control adenovirus-green fluorescence protein (7.9 +/- 0.3) and restoration of the inhibitory effect of para-aminohippurate (% inhibition 34 +/- 4%). These findings indicate that NHERF-1 exerts a significant effect on the renal tubular reabsorption of uric acid in the mouse by modulating the BBM abundance of mURAT1 and possibly other BBM uric acid transporters.     

Electrophysiology of ammonia transport in renal straight proximal tubules.

To test for electrogenic transport of ammonium ions in straight proximal renal tubules, isolated perfused tubules have been exposed to peritubular ammonium ions during continuous recording of cell membrane potential. As a result, 20 mmol/liter NH4+ leads to a rapid, reversible depolarization of the cell membrane by 9.0 +/- 0.3 mV (N = 86). This depolarization is not significantly affected by 10 mmol/liter barium or 0.1 mmol/liter amiloride on both sides of the epithelium, but is significantly blunted by omission of extracellular bicarbonate and CO2 (3.8 +/- 0.4 mV, N = 9), by 1 mmol/liter acetazolamide (4.3 +/- 0.3 mV, N = 11), by 1 mmol/liter peritubular amiloride (4.3 +/- 1.1 mV, N = 7), by 1 mmol/liter SITS (5.7 +/- 0.4 mV, N = 6), and by replacement of extracellular sodium with choline (4.7 +/- 0.5 mV, N = 8). In the presence of both amiloride (1 mmol/liter) and acetazolamide (1 mmol/liter) in the bath, the NH4+ induced depolarization is completely abolished. Furthermore, the combined omission of bicarbonate and addition of 10 mmol/liter barium eliminates the NH4+ induced depolarization. About 50% of the depolarization can be explained by enhanced electrogenic bicarbonate exit due to the intracellular alkalosis. The other 50% is explained by amiloride and barium sensitive electrogenic entry of NH4+ into the cell.     

Renal response to metabolic alkalosis induced by isovolemic hemofiltration in the dog

We describe a new model of chloride-depletion alkalosis (CDMA), in which the method of induction of alkalosis does not itself cause a direct alteration in sodium and fluid balance. We have used this model, which is based on hemofiltration techniques in the dog, to study the immediate response of the kidney to the induction of CDMA. Normal dogs maintained with a NaCl-free diet for several days underwent hemofiltration of 50 ml/kg over a 35 minute period. The hemofiltrate was replaced ml for ml with a solution containing sodium and potassium in the same concentrations as found in each animal's plasma water. In control animals, the replacement solution contained chloride and bicarbonate in the same ratio as in the plasma; in the experimental (CDMA) animals the replacement solution contained bicarbonate as the only anion. In the control group, the procedure of hemofiltration coupled with isovolemic replacement caused no appreciable changes in plasma composition, urinary excretion rates, GFR, or tubular handling of bicarbonate. In the CDMA group, 106 +/- 8.4 mEq of chloride were removed in exchange for bicarbonate. A marked metabolic alkalosis resulted, plasma bicarbonate concentration increasing from 21.9 +/- 0.6 to 33.3 +/- 0.6 mEq/liter. The hemofiltration procedure itself, by design, did not alter sodium or fluid balance. Nevertheless, cumulative urinary sodium excretion increased over 2.5 hours by 23.0 +/- 6.4 mEq. A natriuresis of this magnitude is equivalent to a loss of ECF volume of approximately 200 ml. GFR did not change significantly. The rate of tubular reabsorption of bicarbonate increased significantly from 1209 +/- 82 to 1559 +/- 148 mu Eq/min in CDMA animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

The importance of renal net acid excretion as a determinant of fasting urinary calcium excretion

To evaluate the effects of changing rates of fixed acid production on fasting urine Ca/creatinine, we studied five healthy men fed constant diets during control conditions (serum HCO3 27.3 +/- 2.6 SD mEq/liter and blood H+ 40.4 +/- 1.5 microEq/liter) and then during the administration of NH4Cl 3.0 mEq/kg/day (serum HCO3 22.5 +/- 4.9 mEq/liter; P less than 0.025, and H+ 46.8 +/- 2.3 mEq/liter; P less than 0.005). In addition to the expected increase in daily urinary Ca excretion from 5.2 +/- 2.0 to 12.5 +/- 3.0 mmole/day; P less than 0.001 as daily urinary net acid excretion was increased from 48 +/- 32 to 257 +/- 33 mEq/day; P less than 0.001 we observed that fasting urinary net acid/creatinine excretion also increased from 2.9 +/- 1.2 to 11.1 +/- 1.2 mEq/mmole creatinine; P less than 0.001 and fasting urine Ca/creatinine increased from 0.158 +/- 0.111 to 0.456 +/- 0.109 mmole/mmole creatinine; P less than 0.005. The additional Ca appearing in the urine during acidosis ultimately reflected augmented net bone resorption since daily urinary hydroxyproline excretion was increased from 0.232 +/- 0.062 to 0.377 +/- 0.108 mmole/day; P less than 0.01. Since variations in diet composition can cause fixed acid production and thus renal net acid excretion to vary from about zero to 200 mEq/day, such a range could cause fasting Ca/creatinine to vary from 0.09 to 0.37 mmole/mmole (0.03 to 0.13 mg/mg) and should be taken into account in the evaluation of fasting Ca/creatinine.     

Abnormal circadian rhythm of diuresis or nocturnal polyuria in a subgroup of children with enuresis and hypercalciuria is related to increased sodium retention during daytime

PURPOSE: In a subgroup of children with enuresis an increase in nighttime water and solute excretion has been documented. To investigate if modifications in renal function are involved in nocturnal enuresis, we assessed circadian variation in natriuresis and tubular sodium handling in polyuric hypercalciuric children. MATERIALS AND METHODS: A total of 10 children with proved hypercalciuria and nocturnal polyuria and 10 age matched controls were included in the study. A 24-hour urine collection was performed in 8 sampling periods for measurement of urinary sodium excretion. Segmental tubular sodium transport was investigated during a daytime oral water load test and calculated according to standardized clearance methodology. RESULTS: The children with enuresis showed a marked increase in the fractional excretion of sodium during the night (0.93% +/- 0.36%), while daytime sodium excretion was decreased (0.84% +/- 0.23%). Analysis of segmental tubular sodium transport revealed decreased delivery of sodium to distal tubule (C(H2O) + C(Na) = 10.7 ml/100 ml glomerular filtration rate), indicating increased proximal tubular sodium reabsorption but also stimulation of distal sodium reabsorption as demonstrated by increased fractional distal sodium reabsorption (92.9% +/- 2.2%, controls 90.5% +/- 2.9%). Increased distal reabsorption was associated with increased fractional potassium excretion (17.5% +/- 2.7%, controls 13.6% +/- 6.4%), indicating increased distal tubular sodium/potassium exchange. CONCLUSIONS: No intrinsic defect in renal tubular sodium transport was found, but during the day increased sodium reabsorption in proximal and distal tubules was observed, suggesting extrarenal factors to be involved in altered circadian variation in solute and water excretion by the kidney.     

Clusterin production in the obstructed rabbit kidney: correlations with loss of renal function.

Clusterin, a protein associated with cell death, has been suggested as a marker of renal injury. Correlation of clusterin gene expression with changes in renal function and quantitative measurement of clusterin protein levels after ureteral obstruction have not been previously reported. With unilateral ureteral obstruction in rabbits as the experimental model, the time course of alterations in renal function, clusterin mRNA accumulation, and concentrations of clusterin protein in serum, urine, and renal tissue were investigated. RBF, GFR, and renal concentrating ability (percent sodium reabsorption and urine osmolarity) all decreased (P < 0.05) in the obstructed kidney from control values within 1 day of ureteral obstruction. Clusterin mRNA levels started to rise in the ipsilateral kidney within 12 h of ureteral obstruction and increased up to 10-fold above control levels after 3 days of obstruction. Hybridization histochemistry showed that clusterin mRNA was initially detectable in collecting ducts and distal tubules within 12 h of ureteral obstruction. After 7 days of obstruction, increased accumulation of clusterin mRNA was also detectable in proximal tubular epithelial cells. Clusterin gene expression remained elevated in collecting ducts after 60 days of obstruction. Clusterin expression in the contralateral kidney was increased twofold over control values after 12 h of obstruction. No increase in clusterin mRNA accumulation was detectable after 24 h in the contralateral kidney. Total clusterin protein in the obstructed kidney increased from 0.59 +/- 0.66 (mean +/- 1 SD) to 2.5 +/- 1.3 micrograms after 7 days of ureteral obstruction (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

The pathogenesis of dysplastic kidney in a urinary tract obstruction in the female fetal lamb

BACKGROUND/PURPOSE: The type of renal dysplasia resulting from obstructive uropathy depends on the completeness of the obstruction and its timing with respect to the stage of glomerulogenesis at the time of the obstruction. The authors created a successful obstructive uropathy model in the female fetal lamb to demonstrate the differing pathogenesis of renal dysplasia. METHODS: Female fetal lambs at 60 and 90 days' gestation had their urethra and urachus ligated transabdominally and were delivered by cesarean section at 145 days (full term). Kidney length and cortical thickness were measured, and samples were examined histologically. In the lambs operated on at 90 days, the urine was collected at delivery and Na and CI were measured and compared with the results obtained from normal full-term lambs. RESULTS: Seven of 10 female lambs had hydronephrosis or dysplastic kidneys. The cortext to kidney length ratio was 10+/-3% in the 90-days hydronephrotic group versus 29+/-6% in the controls (P<.001). Morphologically, the 90-day model had dilatation of the collecting tubules with normal glomerular numbers. The 60-day model had tubular cysts with fibromuscular cuffing and reduced glomerular numbers. The fetal urine Na was 47+/-3.3 mmol/L in controls versus 78+/-24 mmol/L in the hydropnephrotic lambs (P<.05). The urine CI in these lambs was 38+/-8.6 mmol/L in controls versus 55+/-14.5 mmol/L in the hydronephrotic lambs (P<.05). CONCLUSIONS: An obstructive uropathy model was created in female fetal lambs. There were no dysplastic changes in the kidneys in lambs operated on at 90 days' gestation, but there were definite dysplastic changes in those operated on at 60 days. Concentrations of Na and CI in the fetal urine are higher than normal in the 90-day model.     

Regulation of acid-base equilibrium in chronic hypercapnia

Previous studies from this laboratory have demonstrated that the decreased renal bicarbonate reabsorption prevailing during chronic hypocapnia is not mediated by the alkalemia that normally accompanies this acid-base disturbance but by some direct consequence of the change in PaCO2 itself. Based on the reasonable expectation that the mechanisms underlying the kidney's response to primary respiratory disturbances would be similar over the entire spectrum of physiologic carbon dioxide tensions, the present study was designed to assess whether an acidic change in systemic pH is a critical factor in the renal response to chronic hypercapnia. For this purpose, the plasma and renal responses to chronic respiratory acidosis in normal dogs were compared to those in dogs chronically fed a large hydrochloric acid (HCl) load (7 mmoles/kg/day). Exposure to 6% carbon dioxide for 7 days in a large environmental chamber induced a stable increment in PaCO2 which averaged 17 +/- 0.5 and 22 +/- 1.3 mm Hg in normal and HCl-fed animals, respectively. Steady-state plasma bicarbonate concentration rose from 22.0 +/- 0.4 to 27.1 +/- 0.5 mEq/liter in normals and from 14.7 +/- 0.7 to 24.2 +/- 0.8 mEq/liter in the HCl-fed group. As a result of these changes in PaCO2 and plasma bicarbonate, steady-state plasma hydrogen ion concentration rose in normals from 41 +/- 0.8 to 49 +/- 0.9 nEq/liter (pH 7.39 +/- 0.01 vs. 7.31 +/- 0.01) but did not change significantly in the HCl-fed group (55 +/- 1.4 vs. 56 +/- 1.4 nEq/liter; pH 7.26 +/- 0.01 vs. 7.25 +/- 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Glomerular hyperfiltration in experimental diabetes mellitus: potential role of tubular reabsorption

An increase in Na+/glucose cotransport upstream to the macula densa might contribute to the increase in single nephron GFR (SNGFR) in early diabetes mellitus by lowering the signal of the tubuloglomerular feedback, i.e., the luminal Na+, Cl-, and K+ concentration sensed by the macula densa. To examine this issue, micropuncture experiments were performed in nephrons with superficial glomeruli of streptozotocin-induced diabetes mellitus in rats. First, in nondiabetic control rats, ambient early distal tubular concentrations of Na+, Cl-, and K+ were about 21, 20, and 1.2 mM, respectively, suggesting collection sites relatively close to the macula densa. Second, glomerular hyperfiltration in diabetic rats was associated with a reduction in ambient early distal tubular concentrations of Na+, Cl-, and K+ by 20 to 28%, reflecting an increase in fractional reabsorption of these ions up to the early distal tubule. Third, in diabetic rats, early proximal tubular application of phlorizin, an inhibitor of Na+/glucose cotransport, elicited (1) a greater reduction in absolute and fractional reabsorption of Na+, Cl-, and K+ up to the early distal tubule, and (2) a greater increase in early distal tubular concentration of these ions, which was associated with a more pronounced reduction in SNGFR. These findings support the concept that stimulation of tubular Na+/glucose cotransport by reducing the tubuloglomerular feedback signal at the macula densa may contribute to glomerular hyperfiltration in diabetic rats. Glomerular hyperfiltration in diabetic rats serves to compensate for the rise in fractional tubular reabsorption to partly restore the electrolyte load to the distal nephron.     

Effects of magnesium on isolated canine coronary arterial tension

The effects of magnesium on the tension of isolated canine coronary arterial strips were studied. In the solution containing K+ of 20 mEq.l(-1), Ca2+ of 4 mEq.l(-1), and Na+ of 127 mEq.l(-1), the tension was 811 +/- 111 mg with Mg2+ of 1 mEq.l(-1), 494 +/- 135 mg with Mg2+ of 10 mEq.l(-1), 272 +/- 126 mg with Mg2+ of 20 mEq.l(-1), -52 +/- 63 mg with Mg2+ of 30 mEq.l(-1), -69 +/- 80 mg with Mg2+ of 40 mEq.l(-1). In the solution containing K+ of 20 mEq.l(-1), Na+ of 12 mEq.l(-1) and Ca2+ of 0 mEq.l(-1), the tension was 102 +/- 22 mg with Mg2+ of 1 mEq.l(-1), 3 +/- 35 mg with Mg2+ of 10 mEq.l(-1), -49 +/- 33 mg with Mg2+ of 20 mEq.l(-1), -59 +/- 49 mg with Mg2+ of 30 mEq.l(-1), -65 +/- 54 mg with Mg2+ of 40 mEq.l(-1).The data demonstrated that Mg2+ above 30 mEq.l(-1) inhibited the increase in tension caused by Ca2+ and Mg2+ above 20 mEq.l(-1) inhibited the increase in tension caused by low Na+ concentration.     

Glomerular and proximal tubular morphology after single nephron obstruction

This study examined the effect of blocking proximal tubule lumens on glomerular and early proximal tubular morphology. Single nephrons in the rat kidney were blocked with wax by micropuncture. After one day, one week, or one month of obstruction, the kidneys were fixed with glutaraldehyde by intravascular perfusion, and nephron structure was examined by light and electron microscopy. Following obstruction, glomerular changes developed more slowly than tubular changes. After one day, the only change noted in some glomeruli was the presence of inflammatory cells. The only tubule change upstream to the block was a focal loss of apical microvilli. This is in contrast to the severe damage previously reported (Evan, Tanner: Kidney Int 30: 818-827, 1986) in downstream proximal tubule segments at this time. After one month of obstruction, glomerular size was decreased and the glomerular filtration membrane was abnormal. Tubular cell size was decreased, apical microvilli were lost, basolateral interdigitations were reduced, and mitochondria were fewer and abnormally oriented. Interstitial fibrosis was present. Changes in nephron structure develop slowly after obstruction, perhaps because continued filtration and reabsorption maintain nephron integrity. Eventually, blocked nephrons atrophy, probably because of reduced blood flow, disuse, and inflammatory responses.