Micropuncture Studies of Sodium Tranport in the Remnant Kidney of the Dog THE EFFECT OF GRADED VOLUME EXPANSION

Proximal and distal tubule micropuncture studies were performed to examine the response to graded extracellular volume (ECV) expansion in 10 normal dogs (stage I), 11 dogs with a unilateral remnant kidney (stage II), and 7 dogs with a remnant kidney after removal of the contralateral kidney (stage III). Before ECV expansion in stage III, there was a suggestive reduction in proximal tubule as well as loop fractional reabsorption of sodium. After ECV expansion to 3% body weight proximal tubule reabsorption was depressed in all groups of animals, while little further inhibition was observed in this segment with additional expansion to 10% body weight. In contrast, the fraction of filtered sodium remaining in the distal tubule rose progressively in all three groups after graded ECV expansion, suggesting that the graded natriuretic response found in the final urine was largely due to a similar response in the loop of Henle rather than that in the proximal tubule. The distal tubule response of the remnant kidney in both stages II and III was greater than that in stage I. These data indicate that although enhanced sodium excretion per nephron in chronic renal failure may be related to uremia, its exaggerated response to ECV expansion is due, at least in part, to certain as yet unidentified intrarenal factors consequent to reduction in functioning renal mass.     

A Micropuncture Study of Postobstructive Diuresis in the Rat

In order to investigate the syndrome of postobstructive diuresis, clearance and micropuncture studies were carried out in rats after relief of 24 hr of bilateral (BUL) or unilateral (UUL) ureteral ligation. In rats with BUL, a striking diuresis and natriuresis occurred when the obstruction to one kidney (the experimental kidney) was relieved. The results were not influenced by administration of vasopressin or d-aldosterone. Whole kidney clearances of inulin and p-aminohippuric acid (PAH) in the experimental kidney were reduced to 10% and 20% of normal, respectively. Superficial nephron inulin and PAH clearances were also reduced, but only to 40% and 45%, respectively. These findings suggest a heterogeneity of nephron function in which deep nephrons were functioning poorly or not at all. To investigate the site of impaired tubular reabsorption in the surface nephrons, absolute and fractional water reabsorption was measured. Absolute reabsorption was found to be decreased all along the nephron. Fractional reabsorption in proximal tubules was normal, as indicated by an average endproximal tubular fluid per plasma inulin (TF/P(In)) of 2.16 vs. 2.30 in controls. TF/P(In) was markedly decreased in distal tubules (2.91 vs. 8.02) and final urine (5.56 vs. 263). These observations indicate that the major sites of impaired sodium reabsorption leading to the diuresis were beyond the proximal tubule.Rats with 24 hr of UUL did not demonstrate a comparable natriuresis or diuresis either spontaneously when the obstruction was relieved or after i.v. infusion of urea. A major difference between the BUL and UUL rats was that prerelease intrarenal hydrostatic pressure was markedly elevated (30.1 mm Hg) in the former but was below normal free-flow values (9.2 mm Hg) in the latter. Thus, elevation of intrarenal pressure during the period of obstruction may be causally related to the natriuresis and diuresis which occurs after the obstruction is relieved.     

A Comparison of the β-Glycosidase Excretion during Kidney Damage Induced by 4-Nitrophenylarsonic Acid and by Rabbit Anti-Rat Kidney Antibodies

Abstract. In a study of the value of urinary enzyme activities as an indication of glomerular or tubular damage, the effects of two nephrotoxic agents (4-nitrophenylarsonic acid and rabbit anti-rat kidney serum) on the urinary excretion of four β-glycosidases were compared using fluorimetric assays with 4-methylumbelliferyl substrates. The electrophoretic mobilities on starch gel of urinary β-galactosidase, β-glucosidase, β-glucosaminidase and β-glucuronidase, at various times up to 26 days after the injection of the nephrotoxins into the rat, were compared with those of the corresponding enzymes present in normal rat urine, kidney and serum. 4-Nitrophenylarsonic acid causes tubular damage characterised by an immediate rise in the rates of excretion of the four β-glycosidases, followed by a return to normal values. In Masugi glomerulonephritis the immediate rise in enzyme excretion is much less marked but greater increases occur after 10 to 12 days. The increases in excretion rate correlate roughly with the stages of the disease. Both glomerular and tubular damage produce characteristic changes in the excretion of all of the enzymes studied, but β-glucosidase appears to be the most useful indicator of kidney tubular damage, as it is the least widely distributed of these enzymes and is not normally found in urine or serum at significant levels of activity.     

Compensatory Adaptation of Bicarbonate Excretion Following Acute Contralateral Kidney Exclusion in the Dog

Changes in the excretion of bicarbonate, sodium and potassium in one kidney after exclusion (complete sudden ligation of renal pedicle) of its partner have been studied in 16 dogs undergoing bicarbonate diuresis. Fluid balance, haematocrit, plasma electrolyte and protein concentrations were maintained constant throughout the experiment. Acute contralateral renal pedicle ligation lead to an immediate increase in bicarbonate as well as water, sodium and potassium excretion by the remaining kidney. The rapid and immediate increase in the fractional and absolute rates of bicarbonate excretion was observed at varying levels of bicarbonate loading, with the greatest response occurring at the highest infusion rate. Sodium, potassium and water excretion also increased in parallel with urinary bicarbonate loss. The increase in bicarbonate excretion was not accounted for by changes in extracellular fluid volume, plasma composition, glomerular filtration rate, effective renal plasma flow, aldosterone and vasopressin. In 8 sham-operated animals, no abrupt increase in sodium and bicarbonate excretion occurred despite similar continued infusion of sodium bicarbonate. It was concluded that exclusion of one kidney induces immediate adaptive excretory changes for sodium and bicarbonate in the remaining kidney, and that these changes are not accounted for by any of the known factors normally regulating sodium and bicarbonate excretion.     

Polymorphisms in the WNK1 Gene Are Associated with Blood Pressure Variation and Urinary Potassium Excretion

WNK1 - a serine/threonine kinase involved in electrolyte homeostasis and blood pressure (BP) control - is an excellent candidate gene for essential hypertension (EH). We and others have previously reported association between WNK1 and BP variation. Using tag SNPs (tSNPs) that capture 100% of common WNK1 variation in HapMap, we aimed to replicate our findings with BP and to test for association with phenotypes relating to WNK1 function in the British Genetics of Hypertension (BRIGHT) study case-control resource (1700 hypertensive cases and 1700 normotensive controls). We found multiple variants to be associated with systolic blood pressure, SBP (7/28 tSNPs min-p=0.0005), diastolic blood pressure, DBP (7/28 tSNPs min-p=0.002) and 24 hour urinary potassium excretion (10/28 tSNPs min-p=0.0004). Associations with SBP and urine potassium remained significant after correction for multiple testing (p=0.02 and p=0.01 respectively). The major allele (A) of rs765250, located in intron 1, demonstrated the strongest evidence for association with SBP, effect size 3.14 mmHg (95%CI:1.23–4.9), DBP 1.9 mmHg (95%CI:0.7–3.2) and hypertension, odds ratio (OR: 1.3 [95%CI: 1.0–1.7]).We genotyped this variant in six independent populations (n=14,451) and replicated the association between rs765250 and SBP in a meta-analysis (p=7×10⁻³, combined with BRIGHT data-set p=2×10⁻⁴, n=17,851). The associations of WNK1 with DBP and EH were not confirmed. Haplotype analysis revealed striking associations with hypertension and BP variation (global permutation p<10⁻⁷). We identified several common haplotypes to be associated with increased BP and multiple low frequency haplotypes significantly associated with lower BP (>10 mmHg reduction) and risk for hypertension (OR<0.60). Our data indicates that multiple rare and common WNK1 variants contribute to BP variation and hypertension, and provide compelling evidence to initiate further genetic and functional studies to explore the role of WNK1 in BP regulation and EH.     

Micropuncture Study of Diuretic Effects on Sodium and Calcium Reabsorption in the Dog Nephron

A close relationship has been observed between the clearance rates of sodium and calcium under a variety of diuretic conditions. The thiazide diuretics act differently in dissociating the renal tubular reabsorption of sodium and calcium. This phenomenon has been further investigated using recollection micropuncture and clearance techniques in a group of 14 dogs subjected to three consecutive experimental phases: expansion to 3% of body weight (BWt) with Ringer's solution, chlorothiazide infusion at 20 mg/kg/h, and furosemide in a prime of 10 mg/kg/ and a 10 mg/kg/h infusion. Diuretic losses were balanced with infusion of equal volumes of Ringer's solution throughout the experiment. Chlorothiazide increased the fractional excretion (FE) of sodium almost threefold while FE(Ca) was not significantly altered. Furosemide increased FE(Na) and FE(Ca) to an approximately equal, and more marked, degree. This dissociation of sodium and calcium reabsorption after chlorothiazide was also evident in the superficial distal tubule, where (tubule fluid/plasma sodium) (TF/P(Na)) increased from 0.32 to 0.49 (P < 0.01) and TF/(ultrafiltrate)UF(Ca) was unchanged (0.35-0.31). Furosemide markedly reduced the transtubular concentration gradient for both sodium (0.86) and calcium (0.94). TF/P(Inul in) decreased progressively from 3.79 to 2.78 to 2.33 in three phases. In the late proximal tubule, chlorothiazide induced a fall of TF/P(Inul in) from 1.57 to 1.44 (P < 0.01), but the ratio TF/UF(Ca): TF/P(Na) was unchanged. Furosemide had no significant proximal effect. It is concluded that acute administration of chlorothiazide reduces sodium reabsorption in the distal hephron, presumably the cortical diluting segment, without affecting calcium reabsorption.     

Micropuncture study of nephron function in the rhesus monkey

The function of the proximal and distal tubule was studied in the rhesus monkey during antidiuresis and during the diuresis after furosemide administration (during which extracellular fluid volume was maintained).     

Polycystic Kidney Disease Re-evaluated: A Population-based Study

A genetic register of all known cases of autosomal dominantpolycystic kidney disease occurring in South and Mid-Wales hasbeen established. In a population of 2.1 million, 209 familieswith affected members were identified, 303 of whom are currentlyalive, 70 on renal replacement therapy. An additional 551 caseswould be predicted amongst family members at 50 per cent and25 per cent risk, giving an apparent prevalence of 1:2459 inthe general population. Five possible new mutations were seenwhere adults with phenotypic autosomal dominant polycystic kidneydisease had both parents alive, age > 55 years with no cystsvisible on ultrasound. The take-on rate for renal replacementtherapy increased during 1970–79 but has apparently reacheda plateau of 4.8 cases per million population per year overthe last 8 years, despite a rapidly increasing acceptance ofuraemic patients as a whole (72/10⁶/year in 1988–89).Considerably more patients with autosomal dominant polycystickidney disease aged over 50 years were started on treatmentin 1980–89 than in 1970–79, but the survival overallimproved with time. All cases of autosomal dominant polycystickidney disease reaching end-stage renal disease are now beingtreated, but the apparent clinical prevalence of this conditionin our region is less than half the supposed gene frequency,suggesting that undiagnosed cases have a benign prognosis.     

Acute Potassium Dichromate Poisoning: A Toxicokinetic Case Study

Case Report: A 48-year-old man drank 150 mL of an aqueous solution containing potassium dichromate 22.5 g in a suicidal attempt and was admitted 7 hours after the ingestion. Hemodialysis was promptly undertaken and chromium concentrations in serum, erythrocytes, and dialysate were determined during the treatment. Chromium elimination in urine was monitored during hemodialysis and the subsequent 400 hours. The total chromium eliminated via hemodialysis and urine was calculated as 36.7 mg or 0.16% of the ingested dose. Spontaneous urinary elimination proceeded according to an open one-compartment model. The elimination half-life was 71.37 hours ± 17.13 hours (95% CI). Chromium elimination from serum followed an open two-compartment model, with the half-lives of 3.16 hours ± 2.63 hours for phase 1 and 50 hours ± 27 hours (95% CI) for phase 2. Calcium-EDTA therapy had no influence on erythrocyte, serum, or urine chromium level. It contributed, however, to a significant increase in chromium elimination rate in the dialysate. Serum zinc was very low at admission and serum zinc, copper, and magnesium were controlled during the initial 30 hours.     

Micropuncture studies of the sweat formation in cystic fibrosis patients

In order to determine whether the precursor solution of sweat is abnormal in cystic fibrosis, osmolality and concentrations of sodium and chloride were measured in fluid obtained by micropuncture from the sweat gland coil of the nail fold of patients with this disease. Osmolality was 323+/-4.8 SE (mOsm/kg of water), sodium concentration was 151+/-1.1 SE (mEq/liter), and chloride concentration was 124+/-6.0 SE (mEq/liter). The sweat:plasma ratio for osmolality averaged 1.1+/-0.015 SE. These values are not significantly different from the corresponding ones obtained previously in normal individuals. It is concluded therefore that the disturbance of sweat gland function as far as electrolytes are concerned is restricted to the excretory ducts.In a second series of experiments the stop-flow pressure which is generated by sweat glands during secretion was measured. Values up to 500 mm Hg were found in both patients and normals. According to van't Hoff's law (DeltaP = RTDeltaC) hydrostatic pressure differences of this magnitude can be generated by the osmotic difference of 27 mOsm/kg of water observed between precursor sweat and plasma in the present experiments. With respect to the mechanism of sweat secretion this finding supports the hypothesis that active solute transport creates an osmotic gradient which causes osmotic water flux.