How tonicity regulates genes: story of TonEBP transcriptional activator.

TonEBP stimulates genes whose products drive cellular accumulation of organic osmolytes and HSP70, which protect cells from the deleterious effects of hypertonicity and urea, respectively. Mice deficient in the TonEBP gene display severe atrophy of the renal medulla because cells failed to adapt to the hyperosmolality. Emerging data suggest that TonEBP plays a key role in the urinary concentrating mechanism by stimulating the UT-A urea transporters and possibly AQP2 water channel. Thus, TonEBP is an essential regulator in the urinary concentrating mechanism. Studies on structural basis of TonEBP function have revealed the structure of the DNA binding domain, and defined the transactivation domains. Molecular mechanisms underlying the nucleocytoplasmic trafficking, transactivation, and phosphorylation in response to changes in tonicity need to be understood in molecular detail. Such knowledge is needed for the identification of the sensor that detects changes in ambient tonicity and signals to TonEBP.

Does albumin preinfusion potentiate diuretic action of furosemide in patients with nephrotic syndrome?

The aim of this cross-over study was to investigate whether albumin infusion before furosemide administration could potentiate the diuretic action of furosemide. Seven patients with nephrotic syndrome were given the following infusions in random order on two separate days: 1) a sham solution followed by 160 mg of furosemide, 2) 100 ml of 20% human albumin followed by 160 mg of furosemide. Urine and serum furosemide concentrations were measured by high-performance liquid chromatography. The increment of urine volume was greater in albumin preinfusion than in furosemide alone. However, the increments of sodium and chloride excretions between furosemide alone and albumin preinfusion were not different. No significant differences in the pharmacokinetic parameters between the two treatments were observed: area under the concentration-time curve (AUC: 12.7+/-2.2 vs 15.1+/-4.4 g/ml hr), total plasma clearance (253+/-41 vs 256+/-54 ml/min), volume of distribution (341+/-34 vs 494+/-153 ml/kg), elimination half life (4.0+/-1.1 vs 4.6+/-0.8 hr), and urine furosemide excretion of the administered amount (16.5+/-7.3 vs 7.5+/-1.6%). In conclusion, these data show that albumin preinfusion potentiated diuresis, but not natriuresis, of furosemide without any change in the pharmacokinetics of the agent in patients with nephrotic syndrome.

Clinical significance of the fractional excretion of anions in metabolic acidosis.

The fractional excretion of anions has been proposed as a new index for the differential diagnosis of metabolic acidosis, identifying the properties of the conjugate base by examining the renal handling of the anion. Here, we investigated clinical significance of the fractional excretion of anions in pathophysiologic diagnosis of metabolic acidosis by measuring urine ammonium (NH4+) excretion, the ratio of A plasma anion gap/delta plasma HCO3- concentration (deltaAG/deltaHCO3-), and fractional excretion of anions in three different groups of metabolic acidosis: acid overproduction (8 patients with lactic acidosis, 8 with diabetic ketoacidosis, 3 with hippuric acidosis following glue sniffing), acid underexcretion (10 patients with chronic renal failure) and normal controls (10 normal volunteers who underwent 3-day NH4Cl loading). As expected, urine NH4+ excretion was higher in overproduction acidosis than in acid-loaded normal controls (88.1 +/- 12.3 vs. 54.0 +/- 3.7 mmol/day, p < 0.05), and it was lower in chronic renal failure than in acid-loaded normal controls (12.8 +/- 1.7 vs. 54.0 +/- 3.7 mmol/day, p < 0.05). The fractional excretion of anions had no difference between overproduction acidosis and chronic renal failure (41.2 +/- 42.8% vs. 41.0 +/- 8.1%). However, the fractional excretion of anions showed significant differences between the subgroups in acid overproduction (lactic acidosis, 4.7 +/- 0.3%; diabetic ketoacidosis, 45.8 +/- 3.1%; hippuric acidosis, 126.0 +/- 14.4%; p < 0.05). The ratio of plasma deltaAG/deltaHCO3- also exhibited significant differences between the subgroups in acid overproduction (lactic acidosis, 1.5 +/- 0.1; diabetic ketoacidosis, 1.0 +/- 0.1; hippuric acidosis, 0.3 +/- 0.1; p < 0.05). There was an inverse linear correlation between the fractional excretion of anions and the ratio of plasma deltaAG/deltaHCO3- (r2 =-0.89, p < 0.05). In conclusion, determination of the fractional excretion of anions may provide a useful clue to the differential diagnosis of metabolic acidosis caused by acid overproduction.

Metabolic acidosis and urinary acidification defect during the course of hemorrhagic fever with renal syndrome.

To evaluate urinary acidification defect and its contribution to metabolic acidosis (MA) during hemorrhagic fever with renal syndrome (HFRS), we serially analyzed acid-base balance and urinary acidification indices in 10 HFRS patients. Data of the patients were compared with those of 8 normal volunteers (NC). MA was observed in 6 of 8 patients in the oliguric phase, 5 of 7 in the early diuretic phase, 8 of 10 in the late diuretic phase and 2 of 9 in the convalescent phase. HFRS patients with MA had a higher plasma anion gap in the oliguric and early diuretic phases than NC and a higher plasma Cl/Na ratio in the late diuretic phase than NC. As compared with acid-loaded NC, HFRS patients had a higher urine pH in the oliguric, early diuretic and late diuretic phases, a higher urine anion gap (UAG) in the oliguric and early diuretic phases and a lower urinary NH4+ excretory rate in the oliguric, early diuretic and late diuretic phases. Overt distal acidification defect was observed in 6 of 8 patients in the oliguric phase, 3 of 7 in the early diuretic phase, 5 of 10 in the late diuretic phase and none of 9 in the convalescent phase. None of the convalescent patients had latent acidification defect. In conclusion, urinary acidification defect is marked in the oliguric and diuretic phases of severe HFRS and may play a role in the development of a high anion gap (AG) metabolic acidosis in the earlier phase and hyperchloremic MA in the later phase, but rapidly recovers in the convalescent phase.

Absence of H(+)-ATPase in the intercalated cells of renal tissues in classic distal renal tubular acidosis.

Proton-secretory defect is thought to be a major pathophysiologic mechanism leading to classic distal renal tubular acidosis (dRTA). However, there have been only two case reports demonstrating the absence of proton pump in renal tissues of the patients with Sjögren's syndrome. This study presents two cases of classic dRTA in which the absence of intact H(+)-ATPase was shown in their renal biopsy tissues by immunohistochemistry using a rabbit polyclonal antibody against the 70 kDa catalytic subunit of H(+)-ATPase from bovine brain clathrin-coated vesicles; one of the cases is diagnosed as subclinical Sjögren's syndrome and the other is idiopathic dRTA. A normal human kidney (NC) and the renal biopsy tissues from a patient with chronic tubulointerstitial nephritus whose proton secretory capacity was intact (DC) were compared as controls. The first patient, a 26-year-old woman, presented with quadriparesis. Her serologic tests revealed positive autoantibodies (ANA, SSA; SSB & RF), and a lower lip biopsy confirmed the diagnosis of Sjögren's syndrome. The second patient, a 43-year-old woman, who initially presented with a pathologic fracture of both femoral necks was referred for an evaluation for hypokalemia by the Department of Orthopedic Surgery. Her renal ultrasonography showed medullary calcification, and no autoantibodies were positive. Serum electrolytes and blood gas analyses of the two patients indicated severe hypokalemia and metabolic acidosis, and proton secretory defects were shown by a failure to lower the urine pH during marked acidemia induced by NH4Cl loading and an abnormally low urine-blood pCO2 difference during bicarbonate administration. While stainings with the anti-H(+)-ATPase antibody in NC and DC were strongly positive in intercalated cells in the connecting tubules and collecting ducts, the tissues from both patients with dRTA were devoid of any anti-H(+)-ATPase staining in the intercalated cells. These results support that the pathophysiologic basis of impaired H+ secretion in idiopathic classic dRTA as well as Sjögren's syndrome is the absence of intact H(+)-ATPase pumps in the intercalated cells.

Evaluation of renal tubular functions in convalescent phase of hemorrhagic fever with renal syndrome.

To evaluate renal tubular functions and to investigate the causative factors of urinary-concentrating defects in the late stage of hemorrhagic fever with renal syndrome (HFRS), 11 HFRS patients in the convalescent phase were studied and compared with 8 acute renal failure (ARF) patients in convalescence (disease controls) and 9 healthy adults preparing for kidney donation (normal controls, NC). Minimal urine osmolality induced by water loading was higher (p < 0.05) in HFRS (89.5 +/- 22.1 mosm/kg) and ARF patients (84.8 +/- 14.7 mosm/ kg) than in NC (47.8 +/- 4.6 mosm/kg), but the solute-free water clearance of HFRS patients (9.0 +/- 1.3%), measured at maximal diuresis, was not different from that of ARF patients (6.7 +/- 1.2%) or NC (10.5 +/- 1.4%). After 12-hour water deprivation + vasopressin stimulation, HFRS had lower urine osmolality (433.7 +/- 31.1 versus 850.0 +/- 35.1 mosm/kg; p < 0.05), urine-to-plasma osmolality ratio (1.47 +/- 0.11 versus 2.91 +/- 0.11; p < 0.05), and solute-free water reabsorption (0.53 +/- 0.07 versus 0.91 +/- 0.12%; p < 0.05) than NC. As compared with ARF patients (1.09 +/- 0.16%) or NC (1.49 +/- 0.16%), HFRS patients (0.43 +/- 0.20%) had lower solute-free water reabsorption measured at maximal antidiuresis induced by water deprivation + vasopressin stimulation + hypertonic saline infusion (p < 0.05). In HFRS, the plasma vasopressin level and plasma vasopressin/osmolality ratio increased from 3.9 +/- 0.8 to 6.1 +/- 1.1 pg/ml and from 0.013 +/- 0.003 to 0.020 +/- 0.004 pg/ml/mosm/kg after 12-hour water deprivation, respectively (p < 0.01). However, neither basal nor stimulated values of the plasma vasopressin level or plasma vasopressin/osmolality ratio was different among the 3 groups. HFRS patients were not different from ARF patients or NC in lithium clearance, urinary-acidifying capacity, and fractional excretions of sodium, potassium and bicarbonate. We conclude that in the convalescent phase of HFRS, the urinary-acidifying ability is not disturbed, the urinary-diluting defect is mild, and the urinary-concentrating capacity is obviously impaired. This study suggests that the most important factor contributing to the urinary-concentrating defect in HFRS is the reduced collecting duct responsiveness to vasopressin.

Temporal changes and reversibility of carbamylated hemoglobin in renal failure.

The detection of carbamylated hemoglobin (CarHb) is known to be useful in determination of the chronicity of uremia. However, the time course of the in vivo reaction between isocyanic acid and terminal valine residues of the hemoglobin chain is not clearly defined. To assess the temporal relationship and reversibility of carbamylation, we prospectively measured CarHb as micrograms of valine hydantoin per gram of hemoglobin (microg VH/g Hb) by high-performance liquid chromatography in 37 patients with acute renal failure (ARF), 53 patients with chronic renal failure (CRF), and six patients with successful kidney transplant. Patients with ARF had a lower median CarHb concentration (53.2 microg VH/g Hb; range, 24.6 to 97.1 microg VH/g Hb) than those with CRF (115.0 microg VH/g Hb; range, 34.6 to 286.5 microg VH/g Hb; P < 0.01), but had a higher value (53.2 microg VH/g Hb; range, 24.6 to 97.1 microg VH/g Hb) than 31 normal controls (36.6 microg VH/g Hb; range, 19.9 to 62.9 microg VH/g Hb; P < 0.05). In patients with ARF, the CarHb concentration positively correlated with the number of days of illness (r = 0.74; P < 0.01). The patients with ARF of 10 or more days' duration had a higher CarHb concentration (68.7 microg VH/g Hb; range, 36.0 to 93.9 microg VH/g Hb) than those with a shorter duration of ARF (33.7 microg VH/g Hb; range, 24.6 to 55.8 microg VH/g Hb; P < 0.01) despite similar blood urea nitrogen and serum creatinine values. However, they had a lower concentration of CarHb (68.7 microg VH/g Hb; range, 36.0 to 93.9 microg VH/g Hb) than CRF patients with comparable serum creatinine values (112.5 microg VH/g Hb; range, 34.6 to 286.5 microg VH/g Hb; P < 0.01). In patients with a kidney transplant, CarHb concentration declined by 19.7% (range, 12.3% to 35.6%) within 2 to 3 weeks after receiving the graft, while the level of hemoglobin increased by 25% (range, 4.0% to 46.6%) during the same period. Therefore, the total blood CarHb (CarHb x hemoglobin concentration) was not significantly changed. We concluded that the in vivo reaction of carbamylation of hemoglobin progressed during the period of uremia, and there might exist some irreversible preformed CarHb in advanced stages of CRF.